Optical power management in an optical network

ABSTRACT

A system for managing signal power levels in an optical network. The optical network comprises a plurality of nodes having logic to receive and transmit optical signals over a plurality of network interconnections. The system includes a method wherein each of the nodes is provided configuration parameters, each of the nodes is configured based on the configuration parameters, power parameter information is exchanged between the nodes, at least some of the nodes are re-configured based on the power parameter information and the steps of exchanging power parameter information and re-configuring at least some of the nodes are repeated until the optical network is fully configured so that the optical signals have selected signal power levels.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority from co-pending U.S. Provisional PatentApplication No. 60/152,480 filed Sep. 3, 1999, the disclosure of whichis incorporated in its entirety herein by reference for all purposes.This application also claims priority from co-pending U.S. ProvisionalPatent Application 60/166,278 filed Nov. 18, 1999, the disclosure ofwhich is incorporated in its entirety herein by reference for allpurposes.

FIELD OF THE INVENTION

The present invention relates generally to information networks, andmore particularly, to the configuration and operation of an opticalnetwork.

BACKGROUND OF THE INVENTION

In an optical network, it is essential that each network element be ableto transport a large number of optical signals that may have varyingpower levels. This is required because signal power levels dynamicallychange as signals are switched and routed throughout the network.

In a two fiber optical bidirectional line-switched ring (OBSLR) network,working and protect channel pairs are routed around the network. As aresult of network switching events, the working and protect channels maybe routed on different signal paths, with each signal path having adifferent loss characteristic. Thus, it is possible that at any givenpoint in the network, a working and protect channel pair can havedifferent signal power levels. This situation can result in increasedbit error rates (BER) on the lower power channel.

FIG. 1 illustrates how path variations due to typical network switchingevents can result in power level variations between working and protectchannel pairs. A working path contains two channels, 1 and 2, withindividual channel power of A as shown at 102. The protect path has twochannels, 3 and 4, with individual channel power of A as shown at 104.In a typical system, the working and protect channels may be routed viadifferent signal paths that have different signal loss characteristics.As a result of the different routing paths, the working and protectchannels may have different signal power levels at some point in thenetwork as shown at 106. For example, after being routed via one path,channels 1 and 2 have channel power of B; and after being routed viaanother path, channels 3 and 4 have channel power of C. After beingmultiplexed together, the channels still maintain their respectivechannel power levels, and have a power level differential as shown at108. The power level differential 108 between the working and protectchannels may result in excessive BERs, since the lower power channelsmay have a signal level that is too low to be adequately transmitted andreceived on the network.

In addition to the signal loss associated with different routing paths,the power level differential 108 between the working and protectchannels may increase when the signals are amplified. For example, theaggregate channels, as shown at 106, may be input to an amplifier thatexperiences saturation effects caused by the relatively high power levelof channels 1 and 2. The saturation effects may result in non-linearamplification which may increase the amplitude differential 108 to causethe resulting amplified signals to appear as shown at 110. Due to thesaturation effects of the amplifier, channels 1 and 2 receive greateramplification than channels 3 and 4. Thus, channels 1 and 2 have channelpower of D, and channels 3 and 4 have channel power of E. The resultingincreased power level differential is shown at 112. This large powerdifferential contributes to increased BERs as the signals are furtherswitched and transmitted around the optical network.

In typical optical networks, each node may be manually configured tooperate in accordance with intended signal routing in the network. Forexample, preset attenuation pads, having a fixed attenuation value, areinserted in signal transmission paths to set signal attenuation aroundthe network.

In addition to the problems associated with path loss and amplifiersaturation, manually configuring each node in an optical networkpresents a number of additional problems. First, manually configuringeach node is prone to errors. Thus, if a node is configured improperly,it must be manually reconfigured again thereby adding costs. Second,each node must be engineered per site. This means that the nodes are notidentically configured, and therefore each node must be customized.Third, it is difficult to upgrade any network components. For example,upgrading a component in a node may affect other components in the node.Changing a node may affect adjacent nodes. Thus, upgrades andmaintenance for manually configured networks is difficult and expensive.Fourth, it is difficult to add nodes to an existing network, since theadded node and each node it affects must be manually configured. Forexample, manual configuration may require nodes to be added in aspecific sequence or introduce a limitation on the number of new nodesthat may be added. Finally, the network may become unstable if due tosignal routing or switching events, the signal levels are not asanticipated when the manual configuration occurred. For example, ifsignal power levels change as a result of a network switching event, theinitial manual configuration of a network element may result in thatelement being unable to handle the new signal power levels.

SUMMARY OF THE INVENTION

The present invention provides a system for managing signal power levelsin an optical network. In one power management strategy provided by theinvention, a consistent output power per wavelength is maintainedbetween neighboring network elements in a OBSLR network. Consistentmeans that the signal power level between network elements will notchange significantly enough, over any switching condition in thenetwork, to affect the ability of the network to carry traffic. Thislocalizes power management within each node since input power levels tothe nodes remain constant. As a result, power management for the networkbecomes a function of each node's internal component configuration andoptical path variations. In this strategy all switching scenarios arefolded into a small set of operating modes.

In another power management strategy provided by the invention, signalpower parameters for different network switching scenarios are tracked.Thus, it is possible to optimize the available signal-to-noise ratio(SNR) in the network at the cost of calculating, storing and exchangingsignal power parameters around the optical network.

In another power management strategy provided by the invention, signalpower parameters for different network switching scenarios arepre-computed and stored. The pre-computed values provide a way fornetwork elements to quickly react to switching events withoutnecessarily having to re-compute parameters as each event occurs.

In an embodiment of the present invention, a method for managing signalpower levels in an optical network is provided. The optical networkcomprises a plurality of nodes having logic to receive and transmitoptical signals over a plurality of network interconnections. The methodcomprising steps of: providing each of the nodes configurationparameters; configuring each of the nodes based on the configurationparameters; exchanging power parameter information between the nodes;re-configuring at least some nodes based on the power parameterinformation; and repeating the steps of exchanging and re-configuringuntil the optical network is fully configured so that the opticalsignals have selected signal power levels.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates how path variations due to typical network switchingevents can result in power level variations;

FIG. 2 shows a portion of an optical network constructed in accordancewith the present invention;

FIG. 3 shows a detailed view of network elements in the optical network100;

FIG. 4 shows a functional diagram of a first type of internal componentconstructed in accordance with the present invention for use in anetwork element;

FIG. 5 shows a parameter table for use with the first type of internalcomponent shown in FIG. 4;

FIG. 6 shows a functional diagram of a second type of internal componentconstructed in accordance with the present invention for use in anetwork element;

FIG. 7 shows a parameter table for use with the second type of internalcomponent shown in FIG. 6;

FIG. 8 shows a diagram of a first network element constructed inaccordance with the present invention;

FIG. 9 shows a method of operating the first network element shown inFIG. 8 in accordance with the present invention.

FIG. 10 shows a diagram of a second network element constructed inaccordance with the present invention;

FIG. 11 shows a method of operating the second network element shown inFIG. 10 in accordance with the present invention;

FIG. 12 shows a diagram of a third network element constructed inaccordance with the present invention;

FIG. 13 shows a diagram of a network element constructed in accordancewith the present invention;

FIG. 14 shows a detailed embodiment of the network element of FIG. 12;

FIGS. 15-18 show detailed embodiments of the network elements of FIG. 3;

FIG. 19 shows a diagram of routing paths through a network element;

FIG. 20 shows a diagram of a network element constructed in accordancewith the present invention for use in a four fiber optical network;

FIG. 21 shows a four node 2 fiber BLSR network constructed in accordancewith the present invention;

FIG. 22 shows a diagram of a node included in the network of FIG. 21;and

FIG. 23 shows a diagram of a VOA control loop constructed in accordancewith the present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The power management strategy of the present invention provides aconsistent output power per wavelength between neighboring networkelements in a OBSLR network. Consistent means that the signal powerlevel between network elements will not change significantly enough,over any switching condition in the network, to affect the ability ofthe network to carry traffic. This localizes power management withineach node since input power levels to the nodes remain constant. As aresult, power management for the network becomes a function of eachnode's internal component configuration and optical path variations.

In one embodiment of the invention, a method and apparatus are providedfor provisioning cross-connections between internal components at eachnetwork element. As these inter-card connections are made, powermanagement modules negotiate the input and output levels over each cardinterface. These levels are computed at each card from neighboringinterface power levels and the optical path loss for the card and arestored in parameter tables. In this fashion, internal connections areused to automatically compute signal power levels at each point along anoptical path through the network element. Thus, each network element cancompute a constant output power level by analyzing the internal opticalpaths that result from protection (or switching) events. A protectionevent is an event wherein signals in the network are re-routed to theirdestinations to overcome network problems, such as damage or loss of asignal link between network elements. At any network element, the cardprovisioning accounts for protection events so that the worst-caseoutput level is guaranteed over all network protection events.

In another embodiment of the invention, it is possible to track not justthe worst case output levels, but individual scenarios associated withdifferent network configurations having particular operating modes andoptical paths. Although this may result in larger parameter tables to beaccounted for, the best possible SNR for the overall network can beachieved.

FIG. 2 shows a block diagram of a portion of an optical network 200constructed in accordance with the present invention. The opticalnetwork 200 will be used to demonstrate how power management islocalized to the network elements in accordance with the presentinvention.

The network 200 comprises nodes or network elements (NE) 202, 204, 206and 208. The nodes are interconnected by signal links 210, 212, 214 and216. The signal links are used to transmit optical signals between thenodes. The signal links are shown as individual links but may comprisebidirectional transmission paths. For example, signal link 212 comprisesa transmit signal path from node 202 to node 206 and a receive signalpath from node 206 to node 202. Using the signal links, optical signalsmay be transmitted around the network over a variety of routing paths.

The nodes are also interconnected by information links 218, 220, 222 and224. The information links are used to transmit information, such asadministrative information or signal parameters, between the nodes. Theinformation links and the signal links may be separate links or may becombined into one link that carries both signals and information. Theinformation links form an Optical Supervisory Channel (OSC) whichconnects all the nodes in the optical network. Using the OSC, networkelements provide information to each other about the signal levels ofsignals being transmitted over the optical network.

The nodes also have parameter inputs shown at 226, 228, 230 and 232. Theparameter inputs are used to input configuration parameters to thenodes. The configuration parameters are used to configure internalcomponents within the node and may be used to determine signal routingand/or signal power levels. Alternatively, a parameter input at one nodecan be used to input configuration parameters for multiple nodes,wherein the node receiving the configuration parameters distributes themto other nodes via the information links. The parameter inputs may becoupled to an information network, such as an Ethernet network, so thatit is possible to download configuration parameters to the nodes via aremote network entity, such as a network administrator shown at 234. Inaddition, the parameter inputs may be coupled directly to localequipment, as shown at 236, to download configuration parametersdirectly to the nodes in a local mode of operation.

Each of the nodes has east and west signal links that are used to add ordrop signals from the optical network. For example, west link 238 isused to add or drop signals that are transmitted over signal link 212and east link 240 is used to add or drop signals that are transmittedover signal link 210.

In one embodiment of the present invention, the output signal powers ofsignals transmitted on the signal links between neighboring networkelements are held at consistent output power per wavelength. This isaccomplished utilizing specialized hardware and software at each networkelement. For example, the signal power levels associated with signalstransmitted over signal link 210 from node 202 to node 204 are held at aconsistent power level per wavelength by hardware and/or softwarelocated at node 202. Node 204, which receives these signals, also useshardware and/or software of the present invention to transmit outputsignals having a consistent power level per wavelength over signal link214 to node 208. As a result, network protection events will not changethe signal power levels between neighboring nodes significantly enoughto affect the ability of the network to carry traffic.

To accomplish power management at each node, a configuration processoccurs wherein each network element provisions its internal componentsto determine output power as a function of network operating modes. Forexample, the network element may operate in a normal mode, where signalsare routed through the element via one path, or the network element mayoperate in a ring switch mode, where signals are routed through thenetwork element via another path. Each of the operating modes for thenetwork element may result in a different routing path for networksignals. Once provisioning of the internal components is complete, thenetwork elements indicate their output power levels associated withvarious operating modes to neighbor nodes via the information linkswhich form the OSC.

After the network elements receive information over the OSC regardingoutput power levels of neighbor nodes, each network element recalculatesthe power levels along its internal optical paths. An adjusted outputpower level may result from the recalculations. Information about theadjusted output power levels is exchanged between network elements overthe OSC. Additional re-calculations occur if necessary. Thus, acontinuous process occurs wherein a network element determines itsoutput power level based on updated input power level indicationsreceived from neighbor elements over the OSC. Eventually, the networkelements converge on a set of constant internode power levels.

Therefore, a method for performing power management in an opticalnetwork in accordance with the present invention would perform thefollowing steps:

provisioning internal components of each network node as a function ofnetwork operating modes;

determining power parameters for each operating mode at each networknode;

exchanging power parameters between adjacent connected network nodes;

updating the power parameters at each node based on the received powerparameters; and

repeating the steps of exchanging and updating until the nodes convergeon a set of constant internode power levels.

In another embodiment of the present invention, the output signal powersof signals transmitted on the signal links are set to produce the bestpossible SNR for the overall network. To accomplish this, additionalinformation parameters are exchanged between the nodes. The nodes usethe additional information to compute SNR information associated withreceived signals. The nodes then perform internal power managementcalculations to determine how to adjust the received signals so as toachieve the best SNR when transmitting the signals to other nodes.

In another embodiment of the present invention, signal power parametersof signals transmitted on the signal links are pre-computed for some orall switching events that may occur in the network. These pre-computedparameters are then stored for future use. Therefore, instead of havingto spend time re-computing power parameters as switching events occur,the pre-computed values can be used to allow the network elements toquickly adjust to accommodate network switching events.

FIG. 3 shows a detailed view of one embodiment of the network elementsthat make up the network 200. In FIG. 3, the parameter inputs and OSClinks are not shown so that the resulting simplified diagram will aid inproviding a clear description of the components used in the networkelements.

The network elements 202, 204, 206 and 208 are shown broken intosub-components consisting of variable optical attenuators (VOA) 310,optical multiplexers (WDM) 312, optical demultiplexers 316, opticalamplifiers 314 and ring switch modules 301, 302, 303 and 304. Thenetwork elements are shown having slightly different componentarrangements which demonstrates that each network element can beflexibly configured to suit various network applications withoutdeviating from the scope or operation of the present invention.

The VOAs 310 are used to attenuate optical signals by adjustableattenuation factors. For example, an optical signal having a level of −5dBm may be attenuated by 5 dB to produce an output signal having a levelof −10 dBm. The optical multiplexers are used to combine two or moreoptical signals (or channels) into a single optical signal that containsall the channels and maintains their respective power levels. Forexample, working and protect channels may be combined into one signalthat includes both the working and protect channels while maintainingtheir relative power levels. The optical demultiplexers are used tosplit an optical signal into two or more optical signals that mayrepresent component channels. The optical amplifiers are used to amplifyan optical signal to form an amplified optical signal. The ring switchmodules receive one or more input signals, and switches (or redirects)the input signals to one or more signal outputs. The signal links, forexample signal links 210 and 212, are shown as having two signal paths.One path is a clockwise signal path 320 around the network and the otheris a counterclockwise signal path 322 around the network.

The network elements 202 and 204 are shown with VOAs 310 and opticalamplifiers 314 in the signal paths for signal link 210. This arrangementis used to provide additional signal amplification (or attenuation ifnecessary) when the network elements are separated by a great distance.In contrast, the network elements 202 and 206 are shown without theoptical amplifiers 314 in the signal path 212. This arrangement is usedwhen the network elements are close enough together that additionalamplification of the signals is not required but signal attenuation maybe required.

The ring switch modules are used to route optical signals through thenetwork element. In some cases, the optical signals are routed to bypassa network element. For example, to demonstrate how a signal may berouted to bypass a network element, signal 324 enters the west input ofnode 206. The signal 324 is routed along signal link 212 to node 202,and further routed along signal link 210 to node 204 where it exits thenetwork at the east terminal of the node. However, should signal link210 be damaged or otherwise unavailable, ring switch 301 redirects thesignal 324 to form the signal 326. The signal 326 is routed back throughsignal link 212 to node 206 and then routed to node 208 and finally tonode 204. This alternate path allows the original signal to bypasssignal link 210. From this example it is easy to see that the alternatepath may be longer and have a different loss characteristic than theoriginal path. Embodiments of the present invention are designed toaccount for such by-pass operation of the network so that it is possibleto re-route signals while maintaining adequate power levels.

When a signal is routed through a network element, it may experiencesignal loss due to the components within the network element. Thissignal loss may vary based on the different types of components used inthe network element and the routing path of the signal through thenetwork element. As a result, to obtain consistent transmitted signalpower levels, the losses of the internal components of the networkelement and the signal path variations through the network element mustbe accounted for.

Another feature of the present invention is shown at 350. On thetransmission path from node 204 to node 208, VOAs 310 are coupled tosignals prior to being input to the multiplexer 312. The VOAs provideadjustable attenuation to the signals so that their powers can bebalanced before the signals are multiplexed together. Thus, the signalswill have similar power levels when combined and experience similarlosses when transmitted, and if amplified, will not be subject to thenon-linear amplification effects that could result if the signals hadnot been balanced.

In one embodiment of the present invention, several modules are usedwithin a network element to implement local power management. Duringlocal power management, loss values through a network element are basedon nominal loss values for each internal component within the networkelement. However, it is also possible to obtain manufacturer calibrationvalues for each of the internal components, so that exact loss valuesfor each internal component can be derived from the calibration valuesand can be used to determined the loss values for signals routed througha network element.

The active management of power in the system occurs when a conditioncauses optical paths to change drastically. The VOAs control powerfluctuations within each network element. Small power fluctuations areadjusted for automatically by VOA control loops. Power level changeslarger than the relative power of a single wavelength cause the VOA tosuspend attenuation control. The VOAs are alerted to changes in thesystem (e.g. ring switch event or a channel failure), which may resultin local VOA settings being updated to compensate.

The power management controls are:

A VOA positioned before the receive amplifier to control the opticalinput power.

The working and protect paths through a node always experience differentlosses. To compensate, two VOAs equalize the working and protect outputchannels independently before being multiplexed by a working/protectWDM.

The modules used to implement local power management may be implementedvia any combination of hardware and/or software within a networkelement. The following is a brief overview of the modules developed inaccordance with the present invention, with detailed descriptions of themodules provided in other sections of this document.

Power Management Module

A Power Management module runs within each network element. In oneembodiment, the Power Management module comprises a Central PowerManagement (CPM) module running within each node and communicating withProxy Power Management (PPM) modules that run on each card (sometimesreferred to as an internal component) within a node. As internalconnections are provisioned between cards, the CPM determines powerlevels parameters at the card interfaces. In effect, the CPM acts tosimulate how signal power levels will change as signals propagate fromcard to card through the node. The CPM stores these power parameters inits internal memory. The CPM then downloads the power parameters to theindividual PPM modules that run on each card. The PPMs store theparameter information in parameter tables located on each card. Theparameter information is also propagated to CPMs of adjacent nodes sothat power level parameters computed at those nodes can account for thepower levels of signals to be transmitted to them.

In another embodiment, a Power Management module runs on each card in anode. As cards are configured, the Power Management modules determinecard edge to card edge power parameters and store this information in aparameter table. The Power Management modules then communicate with eachother to negotiate power levels over each card interface. The PowerManagement modules that run in cards located at the east and west end ofa node communicate the power parameters to upstream and downstreamnodes.

Variable Optical Attenuator (YOA) Module

The VOAs are located on selected cards within each network element. EachVOA has a control loop that monitors input and output signal powerlevels. The VOAs provide adjustable attenuation and can respond quicklyto small changes in the input power level to maintain a target outputpower level. The VOAs are used in association with several powermanagement functions within the network element to guarantee that thenetwork elements output consistent output power per wavelength.

Switching Module

A Switching Module operates in each network element to provide networkswitching information within the network element. For example, when anetwork element is required to switch its mode of operation from normalto ring switch, the switching module executing on the concerned networkelement indicates the switch event to associated VOAs and powermanagement modules.

Wavelength Manager Module

A Wavelength Manager module operates in each network element to maintaina global view of wavelength s (channels) in the system and their statuswith respect to routing between source and destination n odes. PeerManagers on network elements indicate wavelength status between nodes.Thus, as the number of channels in a particular signal path changes, theWavelength manager receives the channel status and indicates thisinformation to concerned VOAS and other internal components within thenetwork element.

Equipment Protection Module

An Equipment Protection module operates on each network element tosignal an equipment protection event t o concerned internal components.During an equipment protection event, the internal components switch toan operating mode w hereby signals follow an alternate path within thenetwork element.

Exemplary Internal Components

The following is a description of two internal components constructed inaccordance with the present invention and suitable for use inembodiments of the present invention. Following the description of theinternal components, exemplary embodiments of network elementsconstructed utilizing the internal components are described. Theinternal components described herein are exemplary internal componentsand not intended to limit the type of internal components which can beconstructed in accordance with the present invention.

FIG. 4 shows a block diagram representative of one type of internalcomponent 400 constructed for use in a network element in accordancewith the present invention. The internal component 400 can be designedas a detachable module or removable card that is installable in anetwork element. The internal component 400 comprises a power managementmodule 402 coupled to card logic 404. In one embodiment the powermanagement module is a PPM and operates to communicate with a CPM in anetwork element. In another embodiment the power management module is astand alone PM that can handle power management functions for theinternal component 400, and communication with other PMs located onother internal components within a network element. It will be assumedthat the power management module is a PPM.

A parameter table 406 which contains parameters used during theprovisioning of the internal component is coupled to the PPM.Provisioning is the process of configuring the card logic 404 to routeselected inputs to produce selected outputs based on the operating modeof the internal component. The signal loss is computed for each routeand stored in the parameter table 406.

The card logic 404 is representative of different processing functionsand/or signal routing that the internal component 400 performs. Forexample, the card logic can represent a switch matrix where inputsignals are switched to output signals. Alternatively, the card logiccan represent a signal multiplexer or signal demultiplexer where inputsignals are combined or split apart, respectively, to form outputsignals. The card logic has signal inputs 408, where one or more opticalsignals are input, and signal outputs 410, where one or more signals areoutput. Based on the process performed by the card logic, power levelchanges can occur between the input and output signals due to the signalrouting, signal combining, signal splitting and/or internal losses.

The PPM 402 is coupled to the card logic via control channel 412. ThePPM uses the control channel to select card logic signal paths, routingor processing functions that will operate on the input signals to formthe output signals. For example, the PPM can direct the card logic viathe control channel to combine two input signals to form one outputsignal. In another configuration, the PPM can direct the card logic viathe control channel to split one input signal into two output signals.The card logic optionally includes an add input 414 and a drop output416. The add input is used to add local signals to the card logic forprocessing. For example, local signals provided via the add input may becombined with the input signal to form the output signal. The dropoutput is used to provide a local output signal path, so that forexample, signals split from the input signal by the card logic can beoutput locally.

The PPM 402 includes a network administrative port 418. Theadministrative port 418 can be coupled to a network administrative buswhich may couple the PPM to a CPM and/or a network administrativeentity. The administrative entity may then provide operating informationabout the network element in the data network, and consequently, aboutthe operating mode of the internal component 400. The administrativeport 418 may be coupled to a data network, such as an Ethernet network,which also couples to the administrative entity. The networkadministrative entity can exchange operating parameters with the PPM viathe Ethernet connection. The administrative port 418 can also be coupledto equipment that is local to the network element to allow the networkelement and the internal component 400 to be locally configured andmaintained.

In one embodiment, the PPM 402 communicates via the administrative busto a CPM operating in the network element. The CPM controls the powermanagement in the network element and downloads parameters to the PPMfor storage in the parameter table. In a situation where exact lossvalues for the card logic are stored in the internal component 400,these exact loss values can be transmitted from the PPM to the CPM foruse in performing power management functions, and then additionalparameters can be sent from the CPM to the PPM for use by the internalcomponent.

In another embodiment, where the power management module is a PM, the PMuses the administrative port to communicate with other PMs in thenetwork element. In one embodiment, the PM 402 sends its parameter tableto other PMs operating in other internal components within the networkelement. In return, the PM 402 can receive parameter tables being usedby these other PMs. Thus, it is possible that the PM 402 of the internalcomponent 400 can receive information about the operation of otherinternal components that are connected to it.

In another embodiment, the PM 402 has monitor inputs 422 and 424. Themonitor inputs 422, 424 allow the PM to monitor input and output powerlevels of the card logic. For example, the monitor inputs allow the PMto measure (based on the configuration of the card logic) the powerlevel of an output signal resulting from an input signal having aselected power level. Thus, the PM can use the control input toconfigure the card logic and then measure input and output power levelsto determine signal level changes associated with particular card logicconfigurations. These signal levels are then stored in the parametertable and will eventually be transmitted to other internal components inthe network element. By directly monitoring the input and output powerlevels, the PM can account for power variations due to component aging.

Both the PPM and the PM have a switch control input 426. The switchcontrol input 426 receives switch control information from a switchcontrol module (not shown) within the network element. The function ofthe switch control module is to receive network information regardingoperating modes of the network element in the data network, and thenpass this information via the switch control input 426 to the internalcomponents of the network element. For example, the network element maybe operating in a ring switch mode. The switch control module receivesthis operating information from the network and provides it to theinternal components of the network element. The PPMs (PM) of theinternal components use the switch control information to adjust signalpaths defined by the card logic. As a result, input and output powerparameters may change. For example, the PPM 402 uses the switch controlinformation received at the switch control input 426 to change theoperating mode of the card logic. In doing so, different parameters inthe parameter table reflect the internal component's losscharacteristics.

FIG. 5 shows an exemplary parameter table 500 for use with the internalcomponent 400. The parameter table 500 has five switch modes shown ascolumns labeled, Normal 502, Ring Switch 504, Ring Switch Pass Thru 506,Equipment Switch 508 and other 510. Each of the switch modes hascorresponding input and output power levels shown as rows labeled, Inputlevel 512, Output level 514. An Internal loss 516 is represented in thethird row and shows the loss through the internal component based on theswitch mode. For example, in the Normal switch mode, the expected inputsignal level is −3 dBm and the resulting output signal level is −6 dBm.This represents an internal loss of 3 dB as shown. Thus, the parametertable describes signal power levels as they relate to various operatingmodes of the internal component.

FIG. 6 shows a block diagram for a second type of internal component 600constructed in accordance with the present invention. The internalcomponent 600 includes a VOA 602 and a VOA controller (VOAC) 604 coupledto an input signal 612. The VOA can attenuate the input signal byadjustable attenuation factors to produce an attenuated signal 615. Theattenuated signal is processed by card logic 610 to produce an outputsignal 614. The VOAC couples to the VOA to provide a control loop thatcan adjust the VOA attenuation based on power level changes that occurto the input signal. For example, the VOAC adjusts the attenuation ofthe VOA so that small power fluctuations on the input signal 612 producea constant target power on the attenuated signal 615. The internalcomponent 600 utilizes the VOA 602 to provide the capability to operateover a wide dynamic range of input signal levels. Although the internalcomponent 600 has the VOA coupled to the input signal 612, otherembodiments of internal components may have a VOA coupled to the outputsignal 614 or may have a separate VOA coupled to each of the input 612and output 614 signals. It will be apparent to one with skill in the artthat different arrangements of the VOA and VOAC within the internalcomponent are possible without deviating from the scope of the presentinvention.

The VOAC selects the attenuation factor via an attenuation control line616 coupled between the VOA and the VOAC. Two signal level monitoringinputs 618, 620 couple the input signal 612 and the attenuated signal615 to the VOAC, respectively. The VOAC uses the monitoring inputs 618,620 to detect signal level changes and to adjust the attenuation factorof the VOA to achieve a specific target power level for the attenuatedsignal 615.

The internal component 600 also includes a power management module 606.In one embodiment the power management module is a PPM. In anotherembodiment the power management module is a PM. It will be assumed forthe purpose of the following discussion that the power management moduleis the PPM. A parameter table 608 is coupled to the PPM. The PPM iscoupled to the card logic 610 by a logic control line 632. The cardlogic is representative of logic to route, combine, split or provideother processing of the input signals as necessary to produce the outputsignal 614. The VOAC is coupled to the PPM by a VOAC channel 622, whichallows the PPM to transmit information from the parameter table 608 tothe VOAC. So, for example, based on the operating mode of the internalcomponent 600, the parameter table contains parameters describingexpected input signal levels and resulting signal output levels, theseparameters can be transmitted to the VOAC from the PPM and used todetermine the VOA attenuation setting which result in signal levelsconsistent with the expected input and output signal levels.

The PPM communicates via an administrative bus 626 to a CPM operating inthe network element. The CPM controls the power management in thenetwork element and downloads parameters to the PPM for storage in theparameter table. In a situation where exact loss values for the cardlogic are stored in the internal component 600, these exact loss valuescan be transmitted from the PPM to the CPM for use in performing powermanagement functions, and then additional parameters can be sent fromthe CPM to the PPM for use by the internal component.

In another embodiment, there is no CPM in the network element. Each PM606 is a stand alone module that controls the power management for theirrespective internal component. The PMs of the internal components cancommunicate with each other via the administrative bus and cancommunicate with PMs in other nodes via the OSC which can be accessedvia the administrative bus.

A switch control input 624 is coupled to both the VOAC and the PPM. Theswitch control input is used to provide network switching information,so that, based on the switch mode of the network element, the VOAC canadjust the VOA and the PPM can adjust the card logic if necessary. Forexample, if the network node is to operate in a ring switch mode, theswitch control input indicates this mode to the VOAC and the PPM. TheVOAC can use the switch control information to access selectedparameters from the parameter table to determine VOA attenuationsettings which result in signal levels consistent with the expectedinput and output signal levels.

The network administration port 626 can couple to a networkadministration bus so that a network administrative entity can provideparameter information to the PPM for configuring the card logic 610 andto provide administrative information to the PPM about the operation ofthe network.

A wavelength management input 630 is coupled to the VOAC to provideinformation regarding wavelength status in the data network. Forexample, the input signal may initially comprise four wavelengths(channels), wherein the VOA is configured to receive correspondingsignal power levels. If the number of wavelengths in the input signalchanges, due to a network routing event for instance, the wavelengthmanagement input provides indications of these changes to the VOAC. TheVOAC uses this information to determine if the attenuation factor of theVOA should be adjusted. If so, the VOAC uses the attenuation controlline 616 to adjust the attenuation factor of the VOA to compensate forthe change in the number of wavelengths in the input signal.

Thus, the internal component 600 incorporates the VOA 602 and the VOAC604 to provide flexibility to allow a greater range of input powerlevels to produce acceptable output power levels. In addition, awavelength management input provides information about network routingevents that may affect the number of channels in the input signal, andtherefore affect the power level. Even if the number of wavelengths doesnot change, adjustments to the VOA by the VOAC can be made to respond tochanges in the input signal power caused by routing events or signalloss from other means.

FIG. 7 show an exemplary parameter table 700 for use with the secondtype of internal component 600. The parameter table 700 has five switchmodes shown as columns and labeled, Normal 702, Ring Switch 704, RingSwitch Pass Thru 706, Equipment Switch 708 and other 710. Each of theswitch modes has corresponding input and output power levels show asrows labeled, Input level 712, Output level 714 and Internal loss 716.For example, in the Normal switch mode, the expected input signal levelis −3 dBm and the resulting output signal level is −6 dBm. This resultsin an internal loss of 3 dB as shown.

The parameter table 700 also includes a Number of wavelengths row 718 toindicate the number of wavelengths included in the input signal. Sincethere can be a wide range in the number of wavelengths in the inputsignal, the section of the table shown as 720 can be repeated as neededso that input, output and loss values can be derived for differentnumbers of wavelengths in the input signal. Thus, the parameter tabledescribes signal power levels as they relate to the number ofwavelengths in the input signal and the various operating modes of theinternal component 600.

Exemplary Network Elements

The following is a description of two network elements constructed inaccordance with the present invention and suitable for use inembodiments of the present invention. Following the description of thenetwork elements, exemplary methods of operating the network elements inaccordance with the present invention are described. The two networkelements described herein are exemplary network elements and notintended to limit the type of network elements which can be constructedin accordance with the present invention.

FIG. 8 shows an exemplary network element 800 constructed in accordancewith the present invention. The network element 800 comprises threeinternal components representative of the internal component 400 whichare referenced as 400(1), 400(2) and 400(3). For example, the internalcomponents could be configured as a WDM for 400(1), a switch matrix for400(2) and a WPS for 400(3). The network element 800 is suitable for usein an OBSLR network to receive an optical input signal 802 and producean optical output signal 804.

For clarity, the network element 800 shows details of a signal path inone direction, however it will be apparent to those with skill in theart that the network element 800 may contain additional logic to form asecond signal path in the reverse direction from the one shown. Thelogic which forms the second signal path is shown at 850 and processes asecond input signal 852 to produce a second output signal 854. Thus, thenetwork element 800 is configured to handle two signal paths in theOBSLR network, but only one path is shown in detail to facilitate aclear description.

The three internal components 400(1-3) are coupled together so that theinput signal 802 can be processed by all three internal components toproduce the output signal 804. The input signal 802 is input to a signaldemultiplexer 806 where a network data portion 808 of the input signalis split off and input to internal component 400(1). The signaldemultiplexer also splits off OSC signals which form an OSC bus 810. Asecond signal demultiplexer is shown at 856.

Within the network element 800, Proxy Power Management (PPM) modules402(1-3) run on internal components within the network element. The PPMscommunicate with a CPM 826 module via a network administrative bus 828.The CPM models the operation of the internal components and can computeinput and output power levels of the internal components based on theirrespective operating modes. As inter-card connections are established,the CPM computes input and output power levels over each interface anddownloads the parameters into the parameter tables 406(1-3) associatedwith the PPMs.

Depending on the specific card, the CPM may have several interfaces forwhich it must model. Each interface specifies:

The average input power level per wavelength received at an interface.

The average output power level per wavelength transmitted from theinterface. The output power level is calculated based on inputs fromother card interfaces, the internal configuration of the card and itsassociated loss, and the internal path loss between each. interface.

Each card connection along an optical path has power informationassociated with it. The complete path can be traced to the boundary ofthe network element. Whenever a change occurs anywhere along the path(e.g. a card is removed or added, or the input power level changes atthe network element boundary), for all connections that are impacted theCPM recalculates the interface power levels and downloads the newparameters to the associated parameter tables. This allows the CPM toadapt the network element to changes in configuration duringinstallation and hardware upgrades.

In one embodiment, the power management strategy requires that eachnetwork element signal its output average power level per wavelength todownstream neighbors. Based on internal connections, the CPM analyzesthe internal optical paths that result from protection switching. Theworst-case output level is signaled to the downstream neighbor. Thesecalculations ensure a consistent output level from the network elementover all network protection events. Fluctuations, though, are expectedduring provisioning of the system toward a complete ring. Whether theCPM monitors a constant output power to the next node depends on theadministrative state.

In another embodiment, the power management strategy requires that eachnetwork element compute signal power levels to achieve the best possibleSNR for the overall network. Based on received parameter information,the CPM analyzes the internal optical paths to determine how to adjustreceived signals to obtain the best possible SNR.

In another embodiment, power parameters at each network element arecomputed in advance for some or all possible network switching events.These precomputed values are stored for future use. As a result, whennetwork switching events occur, the network element access the storedparameters which allows them to quickly adjust to switching events. Thetime needed to calculate power parameters as switching events occur issaved.

The CPM supports a duplicate set of power parameters used forforecasting upgrade scenarios. These forecast power levels aremaintained by all cards and signaled around the ring between networkelements. This supports the addition of amplifiers or additional networkelements to the ring (during a protection switch condition) with allpower levels recomputed ahead of time. Then as new components arebrought into the traffic path, the forecast values become the new valuesused to adjust the internal component settings of elements around thering.

The following is further description of the network element 800. Thedata portion 808 of the input signal undergoes processing by card logic404(1) to produce a first output 812. The first output 812 is input tothe internal component 400(2) where it is processed by card logic 404(2)to produce a second output 814. An add signal input 816 couples to thecard logic 404(2) so that optical signals may be added to the firstoutput signal 812. A drop signal output 818 couples to card logic 404(2)so that signals may be dropped (and locally received) from either thefirst output signal 812, or if desirable, the add input signal 816. Notethat internal components 400(1) and 400(3) may also have add and droplines (see FIG. 4), however, in this example, they are not used and soare not shown in FIG. 8.

The second output 814 is input to internal component 400(3) where it isprocessed by card logic 404(3) to produce the third output signal 820.The third output signal 820 is input to signal combiner 822, where is itcombined with the OSC bus 810 to form the output signal 804, which canbe transmitted over the optical network to an adjacent network element.Another signal combiner is shown at 830.

Each of the internal components 400(1-3) have associated PPMs 402(1-3)and associated parameters tables 406(1-3), respectively. Since theinteraction of the PPMs with their associated card logic has beendescribed above with reference to FIG. 4, it will not be restated here.The PPMs are coupled to the administrative bus 828 so that parametersmay be exchanged between the CPM and PPMs. The PPM can also exchangeinformation with an OSC control module 824 via the administrative bus.The CPM can communicate with the CPMs of other network elements via theOSC bus 810.

The network administration bus 826 couples a network administrativeentity 832 to the CPM and the PPMs of the internal components. Theadministration bus 828 may be any type of information bus or network,such as an Ethernet network. The Network administrative entity may be aremote network application or may be a device or application that islocal to the network element 800 and coupled to the bus 828.

A network switch control 834 couples to the administration bus 828 toreceive network switching information from the network administrativeentity. The network switch control 834 communicates network switchinginformation to the CPM 826. The CPM can further relay this informationto the PPMs associated with each card.

The OSC control 824 coordinates the reception and transmission ofinformation between network elements over the OSC bus 810. For example,the CPM can transmit parameters, indicating the power level of signalstransmitted from the network element 800 to adjacent nodes, via the OSCbus 810.

Thus it is possible for the network element 800 to receive an inputsignal having both a data signal and OSC information, split the twoapart, process the data signal to form an output data signal, processthe OSC information, produce new OSC information, combine the new OSCinformation with the output data signal, and transmit the combinedsignals to another network element in the OBSLR network.

FIG. 9 shows a block diagram of a method 900 for operating the networkelement 800 in an optical network in accordance with the presentinvention. The method 900 provides a configuration process wherein theinternal components 400(1-3) are configured to transport signals overvarious signal paths based on the operating (or switch) modes for thenetwork element. The internal losses for each path are determined andstored in the parameters tables at each internal component Configurationinformation representing all possible output signal levels from thenetwork element is transmitted to an downstream adjacent element.Upstream adjacent elements transmit their configuration information tothe network element 800. The internal components are reconfigured basedon the received information so that new path loss parameters arecomputed based on the received information. The configurationinformation is again exchanged with other network elements. This processcontinues until all the network elements settle on stable configurationvalues, whereby the loss for every path through a network element willbe accounted for.

At block 902, the network element 800 is coupled to the networkadministrative entity via the administrative bus but is not yet coupledto the to data network. As a result, the network element 800 does notreceive input signals from the network fiber nor does the output signalfrom the network element get transmitted on the network fiber to otherelements in the network.

At block 904, the network administrative entity downloads configurationparameters to the CPM 826 and the PPMs of the internal components viathe administrative bus 826. The configuration parameters describe howthe internal components are provisioned to process signals under severaloperating modes. For example, in a normal mode of operation, theinternal component 400(1) may be configured to demultiplex the inputsignal into one or more component signals for input to the internalcomponent 400(2). The internal component 400(2) may be configured to adda new component signal via the add input and may drop one of thecomponent signals via the drop output. The resulting component signalsare input to the internal component 400(3) which may be configured tomultiplex the component signals together to form an output signal fortransmission on the data network.

At block 906, the CPM simulates the configuration of each internalcomponent and computes associated loss parameters for signal pathsassociated with each operating mode. These loss parameters are storedinternally at the CPM

At block 908, the computed loss parameters are transmitted to each PPMfor storage in their respective parameter tables. The path loss for eachcard is entered into the parameter table and represents the loss of thecard logic when operating in specific modes. Thus, at the completion ofblock 908, the parameter tables of the PPMs will describe power losscharacteristics of their respective internal component associated withvarious operating modes.

At block 914, the network element 800 is coupled to the OBSLR network toreceive network inputs signals from upstream nodes and to transmitprocessed signals to downstream nodes. The coupling and decoupling ofthe network element 800 can be accomplished in several ways. The networkelement can be manually connected to the network, by an operatorphysically connecting network fiber to the network element. In anautomated method, the network element is physically coupled to the datanetwork, but the input and output signals of the network element can beindependently switched on and off using switches internal to the networkelement. This allows a network administrator to remotely couple thenetwork element with the data network, by sending instructions over theadministrative network to control the internal switches.

At block 916, the element 800 receives parameters via the OSC channelthat describe the level of the input signal which will be received froman adjacent upstream node (not shown). The upstream node being thenetwork element that transmits signals to the network element 800. Theparameters are received via the OSC bus by the OSC controller 824 andforwarded to the CPM. As this occurs, the CPM outputs parameters overthe OSC to an adjacent downstream node (not shown). Initially theparameters indicate that no signal is presently being transmitted.

As actual data signals are input to the network, and signal power levelsare detected, one or more configuration scenarios may occur. In a firstscenario, shown at A in FIG. 9, the existing configuration of thenetwork element 800 results in acceptable input and output signal levelsfor use in the data network. In a second scenario, shown at B in FIG. 9,the downstream node cannot handle the signal transmitted from thenetwork element 800, and so, requests a power reduction. To compensatefor the excessive signal, the signal levels are adjusted in accordancewith the present invention. In a third scenario, shown at C in FIG. 9,the internal component 400(2) cannot handle the signal received from theinternal component 400(1), and so, requests a power reduction. Tocompensate for the excessive signal, the signal levels are adjusted inaccordance with the present invention. The method 900 demonstrates thethree scenarios in the following description.

At block 918, the scenario A begins when parameter information from anupstream adjacent node indicates signal levels that will be transmittedto the network element 800. The parameters are transmitted over the OSCand received by the OSC controller 824, which in turns forwards them tothe CPM 826. The CPM re-computes the loss parameters for the internalcomponent 400(1) and the determines that the expected signal levels canbe adequately processed by the card 400(1). The CPM stores thesere-computed parameters in its internal storage.

At block 920, the CPM re-computes the input and output loss parametersfor the card 400(2) based on the updates to parameters for the card400(1). The CPM determines that the expected signal levels can beadequately processed by the card 400(2), and so, the CPM stores thesere-computed parameters for 400(2) in its internal storage.

At block 922, the CPM re-computes the input and output loss parametersfor the card 400(3) based on the updates to parameters for the card400(2). The CPM determines that the expected signal levels can beadequately processed by the card 400(3), and so, the CPM stores thesere-computed parameters for 400(2) in its internal storage.

At block 923, the CPM has completed parameter calculations for all theinternal components and downloads these parameters to the PPMs of theinternal components. The PPMs may adjust their respective internalcomponents based on the received parameters.

At block 924, the CPM now knows the expected inputs signal level fromthe upstream node and the loss expected from the internal component 800.The CPM transmits these signal level parameters to a downstream adjacentnetwork element. In accordance with the invention, as the powerparameters propagate down the network, each network element updates itsinternal component parameter tables and the resulting revised parametersare transmitted to the next element in the network. For example, ifpower level updates to the node upstream from the network element 800affect power levels transmitted from the upstream node, then the networkelement 800 would update its internal components to reflect thesechanges and transmit the adjusted parameters to the downstream networkelement.

At block 926, if different parameters are received from the upstreamnode, then the method 900 proceed on path 928 to update the parametertables of the internal components with the newly received parameters. Ifno different parameters are received, then the method 900 continues onpath 930.

At block 932, the data network continues to move toward stabilization.Even though no new parameters were received by the network element 800,other network elements may still be updating their local parameterstables based on newly received parameter information at those nodes.Eventually, the network will completely stabilize when no differentparameter information propagates to any node in the network, whereby allthe network elements have stable parameter tables. At that point, theloss for every signal path in the network will be accounted for.

The scenario B demonstrates how signal level changes are made toaccommodate inadequate signal levels. The scenario B begins when newparameters arrive at the network element 800 from the upstream node. Thenew parameters indicate that the power level of the signal transmittedfrom the upstream node is not as expected by the network element 800.

At block 934, the new parameters are transmitted over the OSC andreceived by the OSC controller 824, which in turns forwards them to theCPM 826. The CPM re-computes the loss parameters for the internalcomponent 400(1) and determines that the expected signal levels can beadequately processed by the card 400(1). The CPM stores thesere-computed parameters in its internal storage.

At block 936, the CPM re-computes the input and output loss parametersfor the card 400(2) based on the updates to parameters for the card400(1). The CPM determines that the expected signal levels can beadequately processed by the card 400(2), and so, the CPM stores thesere-computed parameters in its internal storage.

At block 938, the CPM re-computes the input and output loss parametersfor, the card 400(3) based on the updates to parameters for the card400(2). The CPM determines that the expected signal levels can beadequately processed by the card 400(3), and so, the CPM stores thesere-computed parameters in its internal storage.

At block 939, the CPM has completed parameter calculations for all theinternal components and downloads these parameters to the PPMs of theinternal components. The PPMs may adjust their respective internalcomponents based on the received parameters.

At block 940, the CPM now knows the expected inputs signal level fromthe upstream node and the loss expected from the internal component 800.The CPM transmits these signal level parameters to a downstream adjacentnetwork element over the OSC. In accordance with the invention, as thepower parameters propagate down the network, each network elementupdates its internal component parameter tables and the resultingrevised parameters are transmitted to the next element in the network.

At block 942 the downstream node determines from the newly receivedparameters that the signal level it is to receive from the networkelement 800 is too high and cannot be adequately processed. Thedownstream node transmits a request over the OSC to the network element800 to reduce its output power level. This request is received by theCPM.

At block 944, the CPM determines if the signal level can be reduced atthe card 400(3). However, the card 400(3) does not include a VOA and socannot reduce the signal level.

At block 946, the CPM determines if the signal level can be reduced atthe card 400(2). However, the card 400(2) does not include a VOA and socannot reduce the signal level.

At block 948, the CPM determines if the signal level can be reduced atthe card 400(1). However, the card 400(1) does not include a VOA and socannot reduce the signal level.

At block 950, the CPM notifies the upstream node that it cannot handlethe expected signal power level and requests a decrease in the level.The request is made over the OSC channel.

At block 952, the upstream network element decreases the signal level ofthe input signal. Either the upstream element has logic to decrease thesignal level or the upstream element requests a signal level reductionfrom other network entities further upstream on the transmission pathfor the signal. Once the signal level is decreased, the upstream elementupdates its parameter tables and transmits updated parameters to thenetwork element 800.

At block 954, the updated parameters that are transmitted from theupstream node over the OSC are received by the OSC controller 824, whichin turns forwards them to the CPM 826. The CPM re-computes the lossparameters for the internal component 400(1) and determines that theexpected signal levels can be adequately processed by the card 400(1).The CPM stores these re-computed parameters in its internal storage.

At block 956, the CPM re-computes the input and output loss parametersfor the card 400(2) based on the updates to parameters for the card400(1). The CPM determines that the expected signal levels can beadequately processed by the card 400(2), and so, the CPM stores thesere-computed parameters in its internal storage.

At block 958, the CPM re-computes the input and output loss parametersfor the card 400(3) based on the updates to parameters for the card400(2). The CPM determines that the expected signal levels can beadequately processed by the card 400(3), and so, the CPM stores thesere-computed parameters in its internal storage.

At block 959, the CPM has completed parameter calculations for all theinternal components and downloads these parameters to the PPMs of theinternal components. The PPMs may adjust their respective internalcomponents based on the received parameters.

At block 960, the CPM now knows the expected inputs signal level fromthe upstream node and the loss expected from the internal component 800.The CPM transmits these signal level parameters to a downstream adjacentnetwork element over the OSC. The request to decrease the power levelhas been satisfied so the downstream node can now handle the signallevels transmitted from the network element 800.

The downstream network element propagates its new parameters to otherelements in the network. Each element in the data network exchangesconfiguration parameters as describe above. This negotiation processhappens over a selected time period which may vary depending on thesignificance of the signal level adjustments and the number of networkelements affected.

At block 926, if different parameters are received from the upstreamnode, then the method 900 proceed on path 928 to update the parametertables of the internal components with the newly received parameters. Ifno different parameters are received, then the method 900 continues onpath 930.

At block 932, the data network continues to move toward stabilization.Even though no new parameters were received by the network element 800,other network elements may still be updating their local parameterstables based on newly received parameter information at those nodes.Eventually, the network will completely stabilize when no differentparameter information propagates to any node in the network, whereby allthe network elements have stable parameter tables. At that point, theloss for every signal path in the network will be accounted for.

The scenario C demonstrates how signal level changes are made toaccommodate inadequate signal levels. The scenario C begins whendifferent parameters arrive at the network element 800 from the upstreamnode. The different parameters indicate that the power level of thesignal transmitted from the upstream node is not as expected by thenetwork element 800.

At block 962, the different parameters are transmitted over the OSC andreceived by the OSC controller 824, which in turns forwards them to theCPM 826. The CPM re-computes the loss parameters for the internalcomponent 400(1) and determines that the expected signal levels can beadequately processed by the card 400(1). The CPM stores thesere-computed parameters in its internal storage.

At block 964, the CPM re-computes the input and output loss parametersfor the card 400(2) based on the updates to parameters for the card400(1). The CPM determines that the expected signal levels cannot beadequately processed by the card 400(2). The CPM determines that theanticipated signal level is too high. The CPM stores these re-computedparameters in its internal storage.

At block 966, the CPM determines if the signal level can be reduced atthe card 400(1). However, the card 400(1) does not include a VOA and socannot reduce the signal level.

At block 968, the CPM notifies the upstream node that it cannot handlethe expected transmitted signal level and requests a decrease in thesignal power. The request is made over the OSC channel.

At block 970, the upstream network element decreases the signal level ofthe input signal. Either the upstream element has logic to decrease thesignal level or the upstream element requests a signal level reductionfrom other network entities further upstream on the transmission pathfor the signal. Once the signal level is decreased, the upstream elementupdates its parameter tables and transmits updated parameters to thenetwork element 800.

At block 972, the updated parameters are transmitted from the upstreamnode over the OSC and received by the OSC controller 824, which in turnsforwards them to the CPM 826. The CPM re-computes the loss parametersfor the internal component 400(1) and determines that the expectedsignal levels can be adequately processed by the card 400(1). The CPMstores these re-computed parameters in its internal storage.

At block 974, the CPM re-computes the input and output loss parametersfor the card 400(2) based on the updates to parameters for the card400(1). The CPM determines that the expected signal levels can now beadequately processed by the card 400(2), and so, The CPM stores thesere-computed parameters in its internal storage.

At block 976, the CPM re-computes the input and output loss parametersfor the card 400(3) based on the updates to parameters for the card400(2). The CPM determines that the expected signal levels can beadequately processed by the card 400(3), and so, the CPM stores thesere-computed parameters in its internal storage.

At block 977, the CPM has completed parameter calculations for all theinternal components and downloads these parameters to the PPMs of theinternal components. The PPMs may adjust their respective internalcomponents based on the received parameters.

At block 978, the CPM now knows the expected inputs signal level fromthe upstream node and the loss expected from the internal component 800.The CPM determines expected output signal power levels and transmitsthese signal level parameters to a downstream adjacent network elementover the OSC.

The downstream network element propagates its new parameters to otherelements in the network. Each element in the data network exchangesconfiguration parameters as describe above. This negotiation processhappens over a selected time period which may vary depending on thesignificance of the signal level adjustments and the number of networkelements affected.

At block 926, if different parameters are received from the upstreamnode, then the method 900 proceed on path 928 to update the parametertables of the internal components with the newly received parameters. Ifno different parameters are received, then the method 900 continues onpath 930.

At block 932, the data network continues to move toward stabilization.Even though no new parameters were received by the network element 800,other network elements may still be updating their local parameterstables based on newly received parameter information at those nodes.Eventually, the network will completely stabilize when no differentparameter information propagates to any node in the network, whereby allthe network elements have stable parameter tables. At that point, theloss for every signal path in the network will be accounted for.

FIG. 10 shows an exemplary embodiment of a second network element 1000constructed in accordance with the present invention. The networkelement 1000 is suitable for use in an OBSLR network to receive opticalinput signals 1002 and 1004 and to produces optical output signals 1006and 1008, respectively.

For clarity, the network element 1000 shows logic that forms a signalpath in one direction, for example, the input signal 1002 flows throughthe network element 1000 to form the output signal 1006. It will beapparent to those with skill in the art that the network element 1000comprises logic to form a second signal path in the reverse directionfrom the one shown. The logic which forms the second signal path isshown at 1050 and is designed to receive information from the inputsignal 1004 and to produce information on the output signal 1008. Thus,the network element 1000 is configured to handle two signal paths in theOBSLR network, but only one path is shown in detail to facilitate aclear description.

Three internal components 600(1), 600(2) and 400(4) are coupled togetherto process information from the input signal 1002 to produce informationfor transport on the output signal 1006. The internal components600(1,2) have VOAs 602(1,2) coupled to operate on the input 1002 andoutput 1006 signals, respectively. The input signal 1002 is input to asignal demux 1010 wherein a data signal 1012 is split off the inputsignal 1002 and input to the internal component 600(1). The signal demux1010 also splits off signals associated with an OSC bus 1014. A similardemux 1011 is used in the reverse signal path.

The data signal 1012 is coupled to the internal component 600(1) whichoperates to produce a first output 1016 that is coupled to the internalcomponent 400(4). The internal component 400(4) operates to produce asecond output 1018 which is coupled to the internal component 600(2).The internal component 600(2) operates to produce a third output 1020which is combined with the OSC bus 1014 at signal mux 1022 to producethe output 1006. Thus, signals from the OSC bus are combined withnetwork data signals to extend the OSC bus between upstream anddownstream network elements. A similar signal mux 1023 is provided forsignals in the reverse signal path.

An add input 1024 is provided by the internal component 400(4), so thatlocal signals may be added to the network signal path. A drop output1026 is provided by the internal component 400(4), so that networksignals can be dropped from the network signal path to form localsignals.

The network element 1000 also includes a network administrative bus 1027that couples to the internal components. The administrative bus 1027also couples to several modules which provide additional functionalityto assist in locally managing signal power levels. A switch control unit1028 is coupled to the network administration bus to receive networkswitching information and to provide this information to the internalcomponents via an internal switch bus 1030. The switching informationdescribes various operating modes possible by the network element whileoperating in the optical network. For example, the network element mayoperate in a ring switch mode or may operate in a normal mode. A networkentity 1031 coupled to the administrative bus can select the mode ofoperation for the network element 1000 by providing the appropriateswitching information to the switch control unit 1028, which in turnprovides the switching information to various modules of selectedinternal components, such as the VOACs 604(1,2).

Each VOA 602(1,2) has a control loop implemented by its associated VOACthat monitors the input power to the VOA and adjusts the output power toa constant level based on the number of wavelengths in the input and thetarget output power per wavelength. Normally, the control loop runs inclosed mode to adjust for incremental power changes resulting fromcomponent aging or temperature. A small change in power level results inthe attenuation changing immediately.

For a large power changes, the VOAC assumes something has changed thewavelength distribution or network topology (e.g. a transponder failure,or ring switch). The VOAC automatically opens the control loop and waitsfor an update on what has changed. Inputs from other modules, such asthe switch control module 1030, are used by the VOAC to adjust theattenuation factor of the VOA to account for the changed conditions.After a hold-off period, the VOAC closes the control loop to “fine tune”the output power level of the VOA based on the new settings.

The VOAC maintains the local data required to compute VOA attenuationsettings. This data consists of:

The number of wavelengths through a VOA under normal, equipmentswitching, and ring switching conditions—the number of wavelengths varydue to these events. The administrative entity provides this data aspart of configuring the system. Adjustments to the wavelength numbersare made as wavelength status events are received due to failures in thesystem.

The input power/wavelength for normal and protection scenarios. The PPMon the card provides this information.

The target output power/wavelength at the VOA output. The PPM on thecard provides this information.

The VOAC operates the control loop to provide the ability to set themaximum attenuation to support squelching requirements in during networkswitching.

In one embodiment of the present invention, the control loop for a VOAmeasures the combined optical power at the VOA. It infers the averagepower by dividing the total power by the number of channels it knowsshould be traversing the VOA. The VOA is then adjusted to provide thedesired power at its output. This feedback loop adjusts for variationsin the behavior of the VOA, the transmitter powers of the channels, andlosses in the path leading to the VOA. This calculation depends onknowledge of the number of channels traversing the VOA, which istypically a stable integer. However, in the event of an upstream failure(e.g. source transmitter or fiber break), some channels would disappearfrom the bundle. The calculation, and therefore the VOA adjustment,would be incorrect. Another reason for a change in the number ofchannels through a VOA would be dynamic provisioning of channels in thenetwork. This provisioning might be effected by enabling and disablingtransmitters, optical switching, tuning transmitters to differentwavelengths or tuning optical add/drop components.

One method to handle the change in the number of channels begins bydetecting an abrupt change in the total input power level to the VOA. Ondetecting such a change, which may be outside the range of the normallyexpected variations mentioned above, the feedback loop “opens” andmaintains the current VOA setting (i.e. voltage, current or positioninput into the VOA component). The loop remains open until newinformation is received at the VOAC about the abrupt power change, forexample, information about a change in the number of channels. Afterthis information is received, the loop is “closed” and the VOA outputpower level is adjusted, using the feedback loop, to a new average powercalculated using the new number of channels. If the information updateto the VOAC is delayed, but the power level after the abrupt change isstable, it is possible for the VOA control loop to stabilize the VOAoutput at that power level pending further information.

The switch control 1028 on each network element publishes ring switchevents during protection switching. These events are used to notify theVOACs to adjust the VOA attenuation value based on the appropriate powerlevel and wavelength information for the ring switch event.

A wavelength management unit 1032 is also included in the networkelement 1000. The wavelength management unit 1032 couples to theadministration bus 1027 to receive wavelength information from thenetwork administration. The wavelength management unit distributes thewavelength information to the internal components of the network element1000 via an internal wavelength information bus 1034. The wavelengthinformation describes the number and type of wavelengths (channels) thatare included in the input signal 1002 received by the network element1000. As channels are added or subtracted from the input signal, thesechanges are indicated to the internal components of the network element1000 to allow them to adjust for changes in optical power levels. Forexample, a change in the number of channels received at the input of theinternal component 600(1) is indicated to the VOAC via the wavelengthinformation bus 1034. As a result, the VOAC may adjust the attenuationof the VOA to compensate for the wavelength change.

The wavelength management unit on each network element signals to peersaround the ring as changes occur in wavelength status. The statussignaling follows the path of the wavelength, so that channel failuresare properly reported during ring protection events. Each wavelength isidentified by the operational status of both its source and destinationnode. This wavelength signaling is used to notify network elementsaround the ring whenever a Loss of Signal (LOS) occurs at thedestination, or the source has failed or been turned off. As wavelengthstatus changes, the wavelength manager generates internal wavelengthstatus events to the PPMs. It is also responsible for sourcing the ringstatus signaling for wavelengths that are added or dropped, for exampleat the add input 1024 and drop output 1026.

An OSC controller unit 1036 is also included in the network element1000.

The OSC controller 1036 couples to the administration bus 1027 toreceive configuration information from the network administration andoperates an OSC bus 1014 to couple to the internal components. Theinternal components can exchange parameters with each other via the OSCbus 1014. The OSC bus 1014 couples to the input signals 1002, 1004 andthe output signals 1006, 1008 via demultiplexers 1010, xxx andmultiplexers 1022, xxx respectively, to allow the internal components toexchange parameters with other network elements coupled to the opticalnetwork.

A CPM 1038 is also included in the network element 1000. The CPMcontrols local power management and transmits power parameters toadjacent network elements via the OSC controller 1036.

The internal components 400(4) and 600(1,2) operate as described abovewith reference to FIG. 4 and FIG. 6, to provide signal processing andpower management flexibility to the network element 1000. Since theinternal components 600(1,2) incorporate VOAs, the network element 1000will be able to adjust for changing input and output signal levelrequirements and therefore are suitable to handle network switchingevents wherein the input and output signals may have varying powerlevels. These signals are scaled as necessary, for example, by the VOA602(1) and VOA 602(2), so that processing within the network elementwill result in the output signal 1006 having a selected power level tomeet the power input requirements of the downstream network element.

Although the CPM 1038, switch control 1028, wavelength manager 1032 andthe OSC controller 1036 are shown as being provided in a supervisorymodule 1040 in the network element 1000, all the above may be comprisedof one or more software modules that may run together or individually onone or more processors within the network element. For example, manycomponents within the network element contain processors that can runthe software associated with each of the above modules. Thus, themodules may be distributed to execute on different processors within thenetwork element.

FIG. 11 shows a block diagram for a method 1100 of operating the networkelement of FIG. 10 in accordance with the present invention. The method1100 provides for a configuration process wherein each network elementin the network produces output signals having selected output power forevery network switching event. The internal losses for each path throughthe network element are determined and stored in the parameters tablesat each internal component. Configuration information representing allpossible output signal levels from one network element is transmitted toa downstream element. An upstream adjacent element transmits itsconfiguration information to the network element 1000. Based on thereceived information, new path loss parameters are computed. Updatedconfiguration information is transmitted to the downstream networkelement. This process continues until all the network elements settle onstable configuration values, whereby the loss for every path throughevery network element will be accounted for.

At block 1102, the network element 1000 is coupled to the networkadministrative entity via the administrative bus but is not yet coupledto the to data network. As a result, the network element 1000 does notreceive input signals from the network fiber nor does the output signalfrom the network element get transmitted on the network fiber to otherelements in the network.

At block 1104, the network administrative entity 1031 downloadsconfiguration parameters to the CPM 1038 and the PPMs of the internalcomponents via the administrative bus 1027. The configuration parametersdescribe how the internal components are provisioned to process signalsunder several operating modes. For example, in a normal mode ofoperation, the internal component 600(1) may be configured todemultiplex the input signal into one or more component signals forinput to the internal component 400(4). The internal component 400(4)may be configured to add a new component signal via the add input andmay drop one of the component signals via the drop output. The resultingcomponent signals are input to the internal component 600(2) which maybe configured to multiplex the component signals together to form anoutput signal for transmission on the data network.

At block 1106, the CPM simulates the configuration of each internalcomponent and computes associated loss parameters for signal pathsassociated with each operating mode in each of the internal components.

At block 1108, the computed loss parameters are transmitted to each PPMfor storage in their respective parameter tables. The path loss for eachcard is entered into the parameter table and represents the loss of thecard when operating in a specific mode. This sequence occurs for all theinternal components and is repeated for all the operating modes Thus, atthe completion of block 908, the parameter tables of the PPMs willdescribe power loss characteristics of their respective internalcomponent associated with various operating modes.

At block 1114, with the internal components configured, the networkelement 1000 is coupled to the OBSLR network to receive network inputssignals from upstream nodes and to transmit processed signals todownstream nodes. The coupling and decoupling of the network element1000 can be accomplished in several ways. The network element can bemanually connected to the network, by an operator physically connectingnetwork fiber to the network element. In an automated method, thenetwork element is physically coupled to the data network, but the inputand output signals of the network element can be independently switchedon and off using switches internal to the network element. This allows anetwork administrator to remotely couple the network element with thedata network, by sending instructions over the administrative network tocontrol the internal switches.

Note that the following descriptions describe configuration and powermanagement functions of the network element 1000. Although describedwith a perspective of configuring all the internal components of thenetwork element, the following methods are also applicable toconfiguring one or more newly added internal components to an alreadyconfigured network element. Thus, the following methods can be used toinitially configure a network element or to configure newly addedcomponents to a previously configured element as upgrades occur.

At block 1116, the element 800 receives parameters via the OSC channelthat describe the level of the input signal which will be received froman adjacent upstream node (not shown). The upstream node being thenetwork element that transmits signals to the network element 1000. Theparameters are received by the OSC controller 1036 and forwarded to theCPM. As this occurs, the CPM outputs parameters over the OSC to anadjacent downstream node. Initially the parameters indicate that nosignal is presently being transmitted.

As signals are input to the network, and signal power levels aredetected, one or more configuration scenarios may occur. In a firstscenario, shown at A in FIG. 11, the existing configuration of thenetwork element 1000 results in acceptable input and output signallevels for use in the data network. In a second scenario, shown at B inFIG. 11, the downstream node cannot handle the signal transmitted fromthe network element 1000, and so, requests a power reduction. Tocompensate for the excessive signal, the signal levels are adjusted inaccordance with the present invention. In a third scenario, shown at Cin FIG. 11, the internal component 400(4) cannot handle the signalreceived from the internal component 600(1), and so, requests a powerreduction. To compensate for the excessive signal level, the signallevel is adjusted in accordance with the present invention. The method1100 demonstrates the three scenarios in the following description.

At block 1118, the scenario A begins when parameter information from anupstream adjacent node indicates signal levels that will be transmittedto the network element 1000. The parameters are transmitted over the OSCand received by the OSC controller 1036, which in turns forwards them tothe CPM 1038. The CPM re-computes the loss parameters for the internalcomponent 400(1) and the determines that the expected signal levels canbe adequately processed by the card 400(1). The CPM stores there-computed parameters internally.

At block 1120, the CPM re-computes the input and output loss parametersfor the card 400(4) based on the updates to parameters for the card600(1). The CPM determines that the expected signal levels can beadequately processed by the card 400(4), and so, stores the parametersassociated with the card 400(4) internally.

At block 1122, the CPM re-computes the input and output loss parametersfor the card 600(2) based on the updates to parameters for the card400(4). The CPM determines that the expected signal levels can beadequately processed by the card 600(2), and so, stores the parametersassociated with the card 600(2) internally.

At block 1123, the CPM has completed parameter calculations for all theinternal components and downloads these parameters to the PPMs of theinternal components. The PPMs may adjust their respective internalcomponents based on the received parameters.

At block 1124, the CPM now knows the expected inputs signal level fromthe upstream node and the loss expected from the internal components ofthe network element 1000. The CPM also determines the expected outputsignal power levels and transmits these signal level parameters to adownstream adjacent network element. In accordance with the invention,as the power parameters propagate down the network, each network elementupdates its internal components' parameter tables and the resultingrevised parameters are transmitted to further downstream elements in thenetwork. For example, if power level updates to a node affect powerlevels transmitted from the node A, that is upstream from the networkelement 1000, the upstream node, then the network element 800 wouldupdate its internal components to reflect these changes and transmit theadjusted parameters to the downstream network element.

At block 1126, if different parameters are received from the upstreamnode, then the method 1100 proceeds on path 1128 to update the parametertables of the internal components with the newly received parameters. Ifno different parameters are received, then the method 1100 continues onpath 1130.

At block 1132, the data network continues to move toward stabilization.Even though no new parameters were received by the network element 1000,other network elements may still be updating their local parameterstables based on newly received parameter information at those nodes.Eventually, the network will completely stabilize when no differentparameter information propagates to any node in the network, whereby allthe network elements have stable parameter tables. At that point, theloss for every signal path in the network will be accounted for.

The scenario B demonstrates how signal level changes are made toaccommodate inadequate signal levels. The scenario B begins whendifferent parameters arrive at the network element 1000 from theupstream node. The different parameters indicate that the power level ofthe signal transmitted from the upstream node is not as expected by thenetwork element 1000.

At block 1134, the different parameters are transmitted over the OSC andreceived by the OSC controller 1036, which in turns forwards them to theCPM 1038. The CPM re-computes the loss parameters for the internalcomponent 600(l) and determines that the expected signal levels can beadequately processed by the logic of card 600(l). The CPM stores theserecomputed parameters in its internal parameter table.

At block 1136, the CPM re-computes the input and output loss parametersfor the card 400(4) based on the updates to parameters for the card600(1). The CPM determines that the expected signal levels can beadequately processed by the logic of card 400(4), and so, stores theserecomputed parameters in its internal parameter table.

At block 1138, the CPM re-computes the input and output loss parametersfor the card 600(2) based on the updates to parameters for the card400(4). The CPM determines that the expected signal levels can beadequately processed by the card 600(2), and so, stores these recomputedparameters in its internal parameter table.

At block 1139, the CPM has completed parameter calculations for all theinternal components and downloads these parameters to the PPMs of theinternal components. The PPMs may adjust their respective internalcomponents based on the received parameters.

At block 1140, the CPM now knows the expected inputs signal level fromthe upstream node and the loss expected from the internal component1000. The CPM determines expected output signal power levels andtransmits these signal level parameters to a downstream adjacent networkelement over the OSC. In accordance with the invention, as the powerparameters propagate down the network, each network element updates itsinternal component parameter tables and the resulting revised parametersare transmitted to the next element in the network.

At block 1142 the downstream node determines that the signal level it isto receive from the network element 1000 is too high and cannot beadequately processed. The downstream node transmits a request over theOSC to the network element 1000 to reduce its output power level. Thisrequest is received by the CPM.

At block 1144, the CPM determines if the signal level can be reduced atthe card 600(2). Since the card 600(2) has the VOA 602(2) coupled to itsoutput, it is possible that the VOA can be adjusted to attenuate theoutput signal to satisfy the request of the downstream node. The CPMre-computes the input and output loss parameters for the card 600(2) inorder to achieve an output signal power level acceptable to thedownstream node and stores these parameters in its internal memory.

At block 1146, the CPM downloads its internal parameters to the PPMassociated with the internal component 600(2). The PPM updates itsparameter table with the re-computed parameters.

At block 1148, the VOAC 604(2) receives the updated parameters from theparameter table via the PPM and adjusts the VOA 602(2) to introduceadditional attenuation to the output signal 1020 in accordance with thenew parameters, thereby reducing the signal power level to satisfy therequest of the downstream node.

At block 1150, the CPM transmits the updated signal level parameters tothe downstream adjacent network element over the OSC.

At block 1152, the downstream network element updates its internalcomponents to adjust to the new input levels and propagates its newparameters to other elements in the network. Each element in the datanetwork exchanges power parameters as describe above. This negotiationprocess happens over a selected time period which may vary depending onthe significance of the signal level adjustments and the number ofnetwork elements affected.

At block 1126, if different parameters are received from the upstreamnode, then the method 1100 proceed on path 1128 to update the parametertables of the internal components with the newly received parameters. Ifno different parameters are received, then the method 1100 continues onpath 1130.

At block 1132, the data network continues to move toward stabilization.Even though no new parameters were received by the network element 1000,other network elements may still be updating their local parameterstables based on newly received parameter information at those nodes.Eventually, the network will completely stabilize when no differentparameter information propagates to any node in the network, whereby allthe network elements have stable parameter tables. At that point, theloss for every signal path in the network will be accounted for.

The scenario C demonstrates how signal level changes are made toaccommodate inadequate signal levels. The scenario C begins whendifferent parameters arrive at the network element 1000 from theupstream node. The different parameters indicate that the power level ofthe signal transmitted from the upstream node is not as expected by thenetwork element 1000.

At block 1162, the different parameters are transmitted over the OSC andreceived by the OSC controller 1036, which in turns forwards them to theCPM 1038. The CPM re-computes the loss parameters for the internalcomponent 600(1) and determines that the expected signal levels can beadequately processed by the logic of card 600(1). The CPM stores theserecomputed parameters in its internal parameter table.

At block 1164, the CPM re-computes the input and output loss parametersfor the card 400(4) based on the updates to parameters for the card600(1). The CPM determines that the expected signal levels are too highto be adequately processed by the logic of card 400(4). The CPM thenlooks upstream from the card 400(4) for a way to reduce the signallevel.

At block 1166, the CPM knows that the card 600(1) includes the VOA602(1). The CPM re-computes the loss parameters for the internalcomponent 600(1) to include additional attenuation from the VOA 602(1)to meet the power level requires of the card 400(4). The CPM storesthese recomputed parameters in its internal parameter table.

At block 1168, the CPM re-computes the input and output loss parametersfor the card 400(4) based on the updates to parameters for the card600(1). The CPM determines that the expected signal levels can beadequately processed by the card 400(4), and so, stores the parametersassociated with the card 400(4) internally.

At block 1169, the CPM re-computes the input and output loss parametersfor the card 600(2) based on the updates to parameters for the card400(4). The CPM determines that the expected signal levels can beadequately processed by the card 600(2), and so, stores the parametersassociated with the card 600(2) internally.

At block 1170, the CPM has completed parameter calculations for all theinternal components and downloads these parameters to the PPMs of theinternal components. The PPMs may adjust their respective internalcomponents based on the received parameters.

At block 1171, the VOAC 604(1) receives the updated parameters from theparameter table via the PPM and adjusts the VOA 602(1) to introduceadditional attenuation to the output signal 1020 in accordance with thenew parameters, thereby reducing the signal power level to satisfy therequest of the card 400(4).

At block 1172, the CPM now knows the expected inputs signal level fromthe upstream node and the loss expected from the internal components ofthe network element 1000. The CPM also determines the expected outputsignal power levels and transmits these signal level parameters to adownstream adjacent network element. In accordance with the invention,as the power parameters propagate down the network, each network elementupdates its internal components' parameter tables and the resultingrevised parameters are transmitted to further downstream elements in thenetwork. For example, if power level updates to a node affect powerlevels transmitted from the node A, that is upstream from the networkelement 1000, the upstream node, then the network element 1000 wouldupdate its internal components to reflect these changes and transmit theadjusted parameters to the downstream network element.

At block 1174, the downstream network element updates its internalcomponents to adjust to the new input levels and propagates its newparameters to other elements in the network. Each element in the datanetwork exchanges power parameters as describe above. This negotiationprocess happens over a selected time period which may vary depending onthe significance of the signal level adjustments and the number ofnetwork elements affected.

At block 1126, if different parameters are received from the upstreamnode, then the method 1100 proceeds on path 1128 to update the parametertables of the internal components with the newly received parameters. Ifno different parameters are received, then the method 1100 continues onpath 1130.

At block 1132, the data network continues to move toward stabilization.Even though no new parameters were received by the network element 1000,other network elements may still be updating their local parameterstables based on newly received parameter information at those nodes.Eventually, the network will completely stabilize when no differentparameter information propagates to any node in the network, whereby allthe network elements have stable parameter tables. At that point, theloss for every signal path in the network will be accounted for.

In the above methods, the computations performed by the CPMs can bevaried to achieve specific network goals. For example, in oneembodiment, the CPMs operate to include calculation of the maximum loss(or minimum power) across the all possible signal paths and operatingmodes, resulting in the storage of the worst case parameters in theparameter table. In this embodiment a small parameter table is requiredand less information needs to be exchanged between network elements,However, the use of the worst case parameters means that in certainmethod steps the network elements are more likely to require a powerlevel decrease.

In the another embodiment, the computational results for all signalpaths for particular operating modes are independently stored, resultingin a table with a multiplicity of entries describing the parameters forthe different paths and modes. The minimum power is calculated over allpaths in particular scenarios, not against all scenarios. In thisembodiment, more table entries are required and more cases must besearched during a switching event to determine the correct parameters touse. More cases have to be exchanged between the networks elements. Thisresults in the best possible SNR for the overall network. Thus, atradeoff results between implementation complexity and SNR.

Real time management of the VOA configurations for a dynamic networkmight more advantageous with one embodiment, while offline calculationof VOA configurations for best SNR might use the other embodiment. Theoffline calculation for network configuration would use multipleinstances of the algorithm described with reference to FIGS. 9 and 10,where the instances of the algorithm would simulate the computation inthe various network elements being configured.

FIG. 12 shows a block diagram of a third network element 1200constructed in accordance with the present invention. The third networkelement 1200 comprises several types of internal components. It will beapparent to a person skilled in the art that the internal components inthe network element 1200, some of which are not described in specificdetail in this document, can be constructed in accordance with thepresent invention in a similar fashion to other internal componentsdiscussed herein. Thus, all manner of internal components suitable foruse in a network element can be constructed by incorporating variousmodules in accordance with the present invention.

Incorporated in the third network element 1200 are line preamps 1202 and1204. The line preamp 1202 receives and transmits optical signals overwest optical fiber 1206 and the line preamp 1204 receives and transmitsoptical signals over east optical fiber 1208. Coupled to the linepreamps are channel Mux/Demux modules 1210 and 1212. The channelMux/Demux 1210 couples to the line preamp 1202 and demultiplexes thereceived input signal into working and protect signals shown at 1214.The channel Mux/Demux 1210 also receives working and protect signalsshown at 1216 and multiplexes them into an output signal fortransmission by the line preamp 1202. The channel Mux/Demux 1212 couplesto the line preamp 1204 and demultiplexes the received input signal intoworking and protect signals shown at 1218. The channel Mux/Demux 1212also receives working and protect signals shown at 1220 and multiplexesthem into an output signal for transmission by the line preamp 1204.

An optical switch matrix 1222 is used by the network element 1200 toswitch signal paths of optical signals received from the east and westfibers 1206, 1208. The optical switch matrix 1222 also switches signalpaths of optical signals received from west transponders 1224 and easttransponders 1226. The transponders provide a way for optical signals tobe dropped from the optical network so that they may be received aslocal signals 1228. The transponders also provide a way for localsignals 1228 to be added to the optical network for transmission toother network elements.

The transponders 1224, 1226 couple to channel Mux/Demux 1230 and 1232,respectively. The channel Mux/Demux 1230, 1232 couple to band Mux/Demux1234, 1236 respectively. The band Mux/Demux 1234, 1236 couple to theoptical switch matrix 1222. The signal paths from the transponders tothe optical switch matrix allows signals to be added or dropped from theoptical network. For example, a local signal received at westtransponders 1224 may be multiplex together with other signals atchannel Mux/Demux 1230 and then may be multiplexed into a signal band atband Mux/Demux 1234. This signal band may be added to the optical signalpath via the optical switch matrix 1222 for transmission on the westfiber 1206. Similarly, signals received from the west fiber 1206 may bedropped from the network by following the reverse path to the westtransponders 1224. The east transponders provide the same finctionalityfor signal on the east fiber 1208.

A band coupling 1238 between the band Mux/Demux 1234 and 1236 providesand an additional signal path to allow signals to cross over from thewest side to the east side. This, in effect, provides a by-pass mode ofoperation. Serving a similar function are channel coupling 1266 andtransponder coupling 1264.

The network element 1200 also couples to a network administration bus1240 to allow a network administrative entity to communicate with themodules of the network element 1200. A switching control module 1242 isprovided within the network element that couples to the administrativebus 1240. The switching control module 1242 receives network switchinginformation and distributes the switching information to selectedmodules in the network element via a switching bus 1244. A wavelengthmanagement module 1246 couples to the administrative bus 1240 andreceives wavelength information about signals transmitted over theoptical network. The wavelength management module 1246 distributes thewavelength information to selected modules within the network element1200 via a wavelength management bus 1248.

A CPM module 1260 is also coupled to the administrative bus 1240 toallow configuration parameters to be downloaded from the network entityto the CPM. The CPM control power management within the element 1200 andcommunicates with PPMs associated with each module (not shown).

The line preamp 1202 operates to multiplex and demultiplex an OSCchannel 1250 with the west transmitted and received optical signals. Theline preamp 1204 functions to multiplex and demultiplex an OSC channel1252 with the east transmitted and received optical signals. The OSCchannels are coupled to OSC controllers 1254 and 1256. The OSCcontrollers distribute information received from other network elementsto the internal components of the network element 1200 via an OSCcontrol bus 1258. The OSC controllers also receive information from theCPM for transmission to other network elements. Thus, informationparameters can be exchanged between the internal components of thenetwork element and other elements in the optical network via the OSCchannel.

All of the internal components of the network element 1200 include PPMs(not shown). The PPMs couple to the administrative bus 1240 to receiveconfiguration parameters from the administrative entity. Theconfiguration parameters are used to configure each of the internalcomponents, so that based on an operating mode, selected input signalsare used to produce selected output signals. Several operating modes maybe configured. For each of the configured operating modes input andoutput power parameters for each of the internal components aredetermined. The power parameters at any particular component representthe signal loss through the component as a result of how it isconfigured.

FIG. 13 shows an embodiment of a network element 1300 constructed inaccordance with the present invention. The network element 1300 includesinternal components 600(4), 600(5) and 400(5). Each of the internalcomponents includes a PM module constructed in accordance with thepresent invention. The PM modules operate to provide power management ina manner similar to the way it is provided in the network element 1000.

In the network element 1300, the PM modules act as stand alone modulesto implement power management strategies at each internal component. Forexample, the PM 1302 module operates to perform power managementfunctions for the internal component 600(4). The PM 1302 thencommunicates power parameters over an administrative bus 1304 to otherPMs in the network element. The PMs in cards located at the upstream anddownstream end of the network element, communicate power parameters toadjacent upstream and downstream network elements, respectively.

FIG. 14 shows a detailed configuration of the network element 1200constructed in accordance with the present invention. Several VOAs areincorporated into the network element 1200, for example at 1402, 1404and 1406.

FIGS. 15-18 shows a detailed configurations of the network elements 202,204, 206 and 208, respectively. The four network elements illustratedifferent configurations of internal components and VOAs that are allsuitable embodiments of the present invention. It will be apparent to aperson with skill in the art that other configurations of networkelements are possible without deviating from the scope of the presentinvention.

Addition of a Network Node

In one embodiment of the present invention, modifications to the powermanagement algorithm support node upgrades. For example, if a node isadded to the network, the power management algorithm adjusts to allow asmooth transition of power levels.

The basic strategy of the power management algorithm is to maintainconstant output power per wavelength between network elements. There areconditions, though, that cause these power “boundaries” to change (i.e.in support for upgrades of network elements to add/remove bands oradd/remove complete network elements from the ring). Whenever one ofthese conditions occurs, the output power per wavelength from eachnetwork element may be required to change.

To prevent disruption of traffic during an upgrade scenario, the powermanagement algorithm allows power levels between network elements tochange, but enforces a slow migration from the current converged set ofnetwork power level and associated VOA attenuation values within eachnetwork element, to a new set. The basis for this migration is that thestarting, migrating, and ending power levels and associated VOA settingsall support traffic in the network. For example, while the VOA settingsare adjusted between the steady-state levels before and after theupgrade, network traffic is constantly supported.

When a new node is added (or removed) from the ring, the networkelements are updated with new connectivity information and sendindications over the OSC channel to neighboring nodes as new wavelengthoutput power levels are computed. The ring will iterate until itconverges on a new set of steady-state power levels and associated VOAsettings (a 2 second hysteresis hold-off is implemented to ensure theloop has converged before notifying VOAs of new target values).

While the convergence occurs, the ring continues to operate with theoriginal set of VOA attenuation values, thus supporting traffic in thenetwork while computing the new values. Once the ring converges on thenew values, the local VOA control loops are notified of new targetvalues for each switch condition. The VOA Control loops enforce the slowmigration by moving to the new target attenuation values over 40increments spaced 200 milliseconds apart. This slow slew rate ensuresthat no power surges occur in the network to disrupt traffic as thenetwork moves to a new power profile. During this migration networktraffic is supported, and this support is maintained while the VOAsincrement to their final settings. When the VOAs reach their finalsettings, the network stabilizes at the new set of converged values,thus completing the upgrade without affecting the flow of traffic in thenetwork.

Wavelength Provisioning

The objective is to allow cards to be added and interconnected without acentral TC application to coordinate power levels between cards. Thelevels specified in and out of each card are encapsulated in thecross-connect and upstream/downstream connection models for that card.

Just provisioning a card in the system has no affect on power levelsbetween cards. Only when a connection is defined (e.g. cross-connect orupstream/downstream connectivity pointers) do cards exchange powerinformation to set the average power levels between them.

A card's average output specifies the average input for the downstreamcard. As the input level changes for a card, it computes a new averageoutput using the nominal loss through the card. This change iscommunicated to the next card if a connection exists. These powerupdates ripple through connected cards as upstream connections are madeand allow cards to be provisioned and connected in any order.

Local Power Management

The following description provides information on local power managementissues.

Each node around the ring knows input and output average wavelengthpower levels from/to neighbors.

A node manages power internally using its VOAs to adjust power levelsfor a constant output power per wavelength to a downstream node.

The Power Management modules (or proxy PMs) associated with cards withina node exchange power level information whenever a connection is madebetween two points. This includes the power level expected during normalworking, equipment protection, ring protection, ring switched, and ringprotect passthru.

Local power management maintains loss information for all the internalcross connections of a circuit pack. For each connection, the outputpower level for each switching condition is computed using this crossconnection loss.

In one embodiment, the output level is computed as the minimum powerlevel resulting over various paths for normal working, equipmentprotection, ring protection passthru, ring protection switched (both theworking and protect paths), or equipment protect scenarios. The minimumresulting output power level sets the guaranteed output wavelength powerfrom the node. Usually, this result from a ring protection condition andmeans that for normal operation, both the Working and Protect VOAs areadjusting the transmit power to this output level.

In another embodiment, the output power level is computed to produce thebest possible SNR for the overall network.

In another embodiment, the output power levels for some or all networkswitching events are pre-computed and stored. Each network element canaccess these pre-computed values to quickly adapt to changing networkconditions.

FIG. 19 illustrates ten paths that are considered during powermanagement.

Working traffic added on same side of network element.

Working traffic added on opposite side of network element and switchedback during ring protection switch.

Working traffic passthru (should be equalized to working traffic addedon the same side of the network element).

Protect traffic switched back to working (ring protection switch)

Working traffic switched back to protect (ring protection switch)

Protect traffic passthru (ring protection passthru).

Protect access traffic add same side

Protect access traffic passthru,

Working traffic added on same side during equipment protection.

Working traffic passthru during equipment protection

In the case of a passthru node, the ring protect switch case involvesanalyzing two paths—incoming working traffic switched back onto theprotect path and incoming protect traffic switched back onto the workingpath. These paths offer differing losses to the incoming signal becausethe BWDM modules have different directional losses.

A node maintains a constant average output power. The only time anetwork element output power level may change is during a configurationupgrade in the network (e.g. adding a Band or inserting a new networkelement). When a configuration change causes the output level to change,the node signals downstream neighbor to re-compute internal power levelsusing new input value. This may cause each network element in the ringto re-converge on a new set of power levels (i.e. new internal OVAsettings for each switch condition).

A node continuously monitors changes in input power level. When a changeoccurs, all internal paths adjust input/output levels per card. Theadjustments along the path may cause the WPS to set a new node outputlevel. This change is signaled to the downstream neighbor. Changespropagate around ring until all node input/output levels converge.

To avoid any impact on traffic, all internal VOA attenuation settingsthat update as a result of a re-convergence are changed slowly from theoriginal settings to the new settings.

Ring switch does not result in power level changes in real time. Outputlevels are preset based on worst-case ring switch scenario.

Each card maintains the following power level information for everyinterface it has:

Input level received from connection during normal, equipment, ringswitch local, ring switch passthru; and

Output level transmitted to connection during normal, equipment, ringswitch local, ring switch passthru.

When a connection is made between two interfaces, the cards are notifiedof their neighbors by the Administrative entity.

When received, a card power model determines any restrictions (e.g. BWDMmay notify CWDM output is too high if required to match passthruchannels) and either acknowledges the change to the power levels, orinstructs the sending power model of any required changes to adhere toany restrictions. If sending card can't meet requested level, it sets analarm condition.

The output of the Preamp module requires the consideration of fourpossible restraints to determine the output level for a connection:

1. The gain of the amplifier for the wavelength input levels.

Pout=Pin+G

2. The power saturation level for the EDFA module.

Pin<EDFAout−G−10 Log₁₀ (Nchns*Nmax)

 Where:

Pin is the maximum amplifier input;

EDFAout is the maximum amplifier output;

G is the amplifier gain;

Nmax=Maximum number of Bands through the Amplifier.

 Using the relationship in the previous step, Pout can be solved as;

Pout=EDFAout−10 Log₁₀ (Nchns*Nmax)

3. An equalization of the amplifier output level with that of the firstband added on the opposite side of a passthru node. This preventsunequal wavelength powers between passthru bands and added bands for thenormal case of working traffic passing through the node.

 For example, an upstream node is instructed to reduce output power ifthe incoming level is too high to match added traffic on the other sideof the network element.

Pout−Passthru_loss_from_amplifier=Transmitter_power−add_loss

4. An equalization of the amplifier output level with that of the firstband added on the same side of a passthru node through the loopback inthe RSM. This prevents unequal wavelength powers between passthru bandsand added bands when the node is in a ring switch mode and protecttraffic is looped back to the working traffic.

Pout−Passthru_loss_from_amplifier=Transmitter_power−add_loss

The Preamp output level must be set to the minimum of these possibleoutput levels:

Pout=MIN (Pin+Gain, EDFAout−10 Log₁₀ (Nchns*Nmax),

Opposite_Transmitter_power−add_loss+Passthru_loss_from_amplifier,

Near_transmitter power−add_loss+Passthru_loss_from_amplifier)

FIG. 20 shows a diagram of a network element 2000 constructed inaccordance with the present invention. The network 2000 can perform allof the power management techniques disclosed above with respect to a twofiber network element. Thus, it is possible to construct a four fiberoptical network that includes systems, components, and power managementstrategies in accordance with the present.

Exemplary Embodiment

An exemplary embodiment of an optical power management system includedin the present invention will now be discussed. The optical powermanagement system allows an optical network to reconfigure with no biterror rate (BER) degradation on unswitched channels and a restorationtime typically under 50 ms for switched channels. The implementation isprovided for a 2-fiber bidirectional line switched ring (BLSR) whereoptical switching serves as the prime restoration mechanism.

This embodiment achieves minimal channel disruption by trying tomaintain the optical power per channel for all channels at a constantlevel regardless of the path the channel travels. If the OSNR of eachchannel is within an acceptable range, the BER for a channel will alsobe within an acceptable range. Thus, channel integrity is maintainedwhen the optical path of a channel changes. The received power and OSNRat a receiver are held within an acceptable range by network control ofEDFA and VOA settings.

Implementation Details

This embodiment is implemented in two stages. First, the networkconfiguration is defined. This involves specifying the number of nodes,the traffic pattern, the link parameters and the hardware required ateach node. The first stage also includes determining the varioussettings of VOA and erbium doped fiber amplifier (EDFA) target values.The second stage involves initializing the network and turning on thetraffic. Optical power control within the network is dominated by theclosing/opening of the VOA and EDFA control loops. Once the network hasinitialized, it is ready to handle failure and restoration events.

In the first stage, the network is designed based on the requiredtraffic pattern. As an example, this embodiment will be discussed withreference to a four node ring 2100 representing a 2-fiber BLSR networkas shown in FIG. 21. In ring 2100, one fiber carries clockwise (CW)traffic while the other carries counter-clockwise (CCW) traffic. Trafficis added and dropped at each node with network information passed aroundthe ring on a separate optical service channel. The protection andworking capacity are divided between the available bandwidth of onefiber. As a result, in a WDM system, the number of channels available ina fiber is divided between the working and protection channels.

In a network of this nature, failures such as equipment problems andfiber breaks are protected against by routing the affected workingchannels in the opposite direction around the ring, using protectionchannel capacity. As a result, the number of channels in a fiber canvary during these events. As well, the path that a given traffic channeltakes from a particular transmitter (Tx) to a particular receiver (Rx)can also vary.

In order to solve these issues of varying channel count and varying pathloss, a combination of EDFAs and VOAs are used throughout the network toprovide calculated amounts of gain and attenuation where required. Theend goal is to establish a network where all channels maintain anacceptable BER independent of the different paths taken during theoperation of the network. As shown in FIG. 21, preamps and/or postampsmay be used on incoming and outgoing fibers respectively to providegain. For example, Node 1 shows a preamp 2102 and postamp 2104 on itsEast side but only a postamp 2106 on its West side. The assignment ofamplifiers is dependent upon the span loss and component insertion lossbetween a selected Tx and Rx. The procedure used to determine placementof EDFAs is primarily dependent upon span loss and insertion loss ofpassive components at a node.

One important aspect of the EDFA operation in this embodiment is thatthey are gain locked and gain flattened. Utilizing an amplifier of thisnature ensures all channels experience similar gain for a variation ininput power. This approach ensures minimal gain tilt in the amplifier.Further, the EDFA can handle input power level fluctuations created bydynamic channel add/drop and total fiber failures and restorations.

The second major control mechanism in the network is the VOA. The VOAprovides a variable level of attenuation for all channels passingthrough it. The placement of VOAs at a node is shown in FIG. 22.

Within a node, a VOA is placed both on the incoming traffic and theoutgoing traffic on both sides of the node. In this embodiment, the VOAon the incoming side attenuates all channels. This is shown as VOA 1 and2 in FIG. 22. For the outgoing side, two VOAs are used followed by amultiplexer. This is shown as VOA pairs 3,5 and 4,6 in FIG. 22. Thispair provides the option to attenuate two subsets of channels bydifferent amounts before they are multiplexed. In this embodiment, theprotection and working channels are the subsets. The switching fabricdetermines which protection and working channels are routed out of thenode on both the East and West side. The incoming VOA, listed as 7 inFIG. 22, is also used to prevent overload of a preamp at the node. Theoutgoing VOAs can be used to prevent overload of a postamp used at thenode. An additional VOA is used following the added channels in orderset the new channels to a power level, which is compatible with channelsincoming from the fibers but not being dropped and passed through thenode. A combination of multiplexers and demultiplexers are used tocombine and separate the various optical wavelengths on the add and dropside of the node.

In order to protect against failure events, the traffic in a BLSRnetwork is switched away from the failure point. Thus, each node mustconsider four cases:

1) Normal.

2) Ring switch away from the east side.

3) Ring switch away from the west side.

4) Tandem case where there is a switch some where else in the networkbut not this node.

Each of these cases can cause the number of channels in each VOA at anode to change as well as the optical power for each channel into theVOA. In order to ensure traffic continuity for all channels, a given VOAis set to a different attenuation depending on which case the node isin. Depending on the nature of the network, a given VOA may have adifferent optimal setting for each of the four cases. On the other hand,the situations may exist where a VOA may have the same setting for morethan one case.

In order to determine VOA target values for each case, the pathperformance for each channel under all different switch scenarios isanalyzed. When determining the path performance of each channel, thefiber and component losses are either measured or estimated. As aresult, an optimal attenuation is determined for each VOA for all fourscenarios. In many cases, the attenuation value for a VOA is the samefor a number of cases and as a result, the VOA will commonly jumpbetween only two target values.

These target values can be stored as attenuation values or as an opticalpower per channel. In order to handle these two variations, a circuit2300 for the VOA is implemented as shown in FIG. 23. In this circuit, atap coupler 2302 follows the VOA 2304 with a PIN detector 2310 used tomeasure the total optical power at the output of the VOA 2304. The PINdetector output is sampled with an analog to digital converter (ADC).The result is processed by a microcontroller 2306. When themicrocontroller has information regarding the number of channels throughthe VOA, it can determine the power per channel. This information ispassed from a CPU associated with the node to the microcontroller in theform of new target attenuation's and optical power settings. Theattenuation of the VOA is set by the microcontroller via a digital toanalog converter (DAC) and subsequent gain.

For the design shown in FIG. 23, both the VOA input and the PIN outputare calibrated. This allows two modes of operation for the VOA controlloop. The first is open loop where the VOA provides a target attenuationvalue. In this case, the PIN is not used. The second mode of operationis where the VOA attempts to provide a constant output power. In thiscase, the PIN is used as a feedback mechanism, thus creating a closedcontrol loop. Depending on the network requirements, the VOA circuit mayuse one or both of the open and closed loop capabilities of the circuit.

When the VOA is in attenuation mode, the control loop is open and theVOA is driven to a pre-calibrated value. When the VOA is in powercontrol mode, the control loop is closed and the detector circuitprovides the feedback. In this mode, attempts are made to hold theoutput power for the VOA constant for changes at the input.

Information regarding the switching events occurring in the network ispassed around the ring so that all nodes are made aware of the pathchanges occurring for a wavelength. As shown in FIG. 21, thisinformation is transmitted around the ring on a separate channel,specifically, an optical service channel 2110. Once each node has anupdate on it's status, the new target attenuations and power levels areloaded and converged upon.

In this network, situations can exist where a protection event occurs ata node and the effect of the changes in channel count and channel powerat a VOA can precede the arrival of the network information passedaround the ring through the optical service channel. In events likethese, a VOA at a downstream node will see an optical power fluctuationbefore it is notified of the change through the optical service channel.In order to handle this type of case, an algorithm is implemented wherethe VOA control loop will, if operating in closed loop mode, open toit's current attenuation, if it sees a power delta beyond a certainvalue at the detector. The control loop will hold this attenuation untilit is notified of the new network status or until a timer has expiredand the input is stable again. If a new target power value is provided,the loop in closed and the new output power is converged to. The generalalgorithm is:

A) When the VOA is operated in open loop mode, the VOA is driven to apredetermined attenuation and the drive level is only updated by themicrocontroller. The VOA setting is not affected by changes in inputpower.

B) When the VOA is operated in closed loop mode, the algorithm is asfollows:

1) Startup is in open loop mode with a predetermined attenuation

2) Once the input to the VOA has stabilized, the VOA control loop isclosed and the VOA is adjusted until the target output power isconverged upon.

3) If there is a power delta larger than X dB at the input, the VOAswitches to open loop mode and holds it's current attenuation.

4) If there is a protecton or restoration event, updated targetattenuation is sent to the VOA first. Second, a new target output poweris sent to the VOA. After a period of Y ms, the VOA control loop closesand converges on the new optical output power.

An additional feature included as part of this embodiment is that theVOA on the incoming side of the node accounts for link loss variations.When this VOA is operated in closed loop mode, changes in the fiber spanloss can be accounted for with the VOA, provided the VOA is not alreadyat minimum attenuation.

The end result of using this strategy of EDFAs and VOAs is that thecontinuity of channels can be maintained in an optically switchednetwork where the physical path of the channels changes to protectagainst failures.

This embodiment includes the following features.

1) The implementation uses a combination of open and closed VOA controlloops to maintain constant attenuation and constant optical power perchannel out of the VOA for cases when information regarding the numberof channels through the VOA is both known and unknown.

2) A unique algorithm is used to determine the migration between closedloop and open loop VOA operation. The algorithm is based on power deltasat the input to the VOA and also network information sent to themicroprocessor controlling the VOA loop.

3) A unique algorithm is used to maintain a constant received opticalpower at a receiver for all channels regardless of the optical path thechannel took from a transmitter to a receiver.

4) The network is precalibrated for optical path loss. Specifically, theoptical path loss for all channels is either measured or estimated withthese values being used to set the VOA under open and closed loopconditions for the various switch states a node may be in.

The present invention provides a method and apparatus for managing powerlevels in an optical network. It will be apparent to those with skill inthe art that modifications to the above methods and embodiments canoccur without deviating from the scope of the present invention.Accordingly, the disclosures and descriptions herein are intended to beillustrative, but not limiting, of the scope of the invention which isset forth in the following claims.

What is claimed is:
 1. A method for managing signal power levels ofoptical signals in an optical network, wherein the optical networkcomprises a plurality of nodes having logic to receive and transmit theoptical signals over a plurality of optical fibers, the methodcomprising steps of: providing each of the nodes configurationparameters; configuring each of the nodes based on the configurationparameters; exchanging power parameter information between the nodes;re-configuring at least some nodes based on the power parameterinformation; and repeating the steps of exchanging and re-configuringuntil the optical network is fully configured so that the opticalsignals have selected signal power levels.
 2. A method for managingsignal power levels of optical signals in an optical network so that theoptical signals have selected power characteristics, wherein the opticalnetwork comprises a plurality of nodes that receive and transmit theoptical signals over optical fibers, the method comprising steps of:configuring one or more nodes based on configuration parameters;accessing power parameters relative to one or more nodes; determiningfrom the accessed power parameters if the optical network is fillyconfigured so that the optical signals have the selected powercharacteristics; and re-configuring one or more nodes, when the opticalsignals do not have the selected power characteristics.
 3. The method ofclaim 2, further comprising a step of repeating the steps of accessing,determining and re-configuring until the optical network is fillyconfigured so that the optical signals have the selected powercharacteristics.
 4. The method of claim 2, further comprising a step ofrepeating the steps of accessing, determining and re-configuring untilthe optical network is fully configured so that the optical signals havethe selected power characteristics, wherein the selected powercharacteristics occur when the optical signals have a consistent outputpower per wavelength between neighboring nodes.
 5. The method of claim2, further comprising a step of repeating the steps of accessing,determining and re-configuring until the optical network is fillyconfigured so that the optical signals have the selected powercharacteristics, wherein the selected power characteristics occur whenthe optical signals have a selected signal-to-noise ratio.
 6. The methodof claim 2, further comprising a step of repeating the steps ofaccessing, determining and re-configuring until the optical network isfully configured so that the optical signals have the selected powercharacteristics, wherein the selected power characteristics occur whenselected signal channels of the optical signals are balanced to haveselected power ratios.
 7. The method of claim 2, further comprising astep of using the power parameters to adjust a selected node tocompensate for power level changes that occur in the network due achange in network conditions.
 8. The method of claim 2, wherein the stepof accessing comprises a step of receiving the power parameters from atleast one neighbor node.
 9. The method of claim 8, wherein the step ofreceiving comprises a step of receiving the power parameters at aselected node from at least one neighbor node, wherein the powerparameters includes a transmit power level parameter.
 10. In an opticalnetwork comprised of a plurality of nodes having logic to receive andtransmit optical signals over optical fibers, a method for managingsignal power levels of the optical signals received and transmitted froma selected node, the method comprising steps of: configuring theselected node based on configuration parameters; receiving powerparameter information describing power levels of the optical signals tobe received at the selected node; determining from the power parameterinformation if the optical signals to be received at the selected nodehave selected power characteristics; and re-configuring the selectednode, when the optical signals do not have the selected powercharacteristics.
 11. The method of claim 10, further comprising a stepof repeating the steps of receiving, determining, and re-configuringuntil the optical signals to be received at the selected node have theselected power characteristics.
 12. The method of claim 10, furthercomprising a step of repeating the steps of receiving, determining, andre-configuring until the optical signals to be received at the selectednode have a selected signal-to-noise ratio.
 13. The method of claim 10,further comprising a step of repeating the steps of receiving,determining, and re-configuring until selected signal channels of theoptical signals are balanced to have selected power ratios.
 14. Themethod of claim 10, further comprising a step of repeating the steps ofreceiving, determining, and re-configuring until the optical signalsreceived at the selected node have a consistent output power perwavelength.
 15. The method of claim 10, wherein the step ofre-configuring comprises steps of: re-configuring the selected node,when the optical signals do not have the selected power characteristics;storing re-configuration information generated when the node isre-configured; and using the stored re-configuration information toadjust the selected node to compensate for power level changes thatoccur in the network due a change in network conditions.
 16. The methodof claim 10, further comprising steps of: transmitting power parameterinformation describing power levels of the optical signals to betransmitted from the selected node; determining if the optical signalsto be transmitted from the selected node have selected powercharacteristics; and re-configuring the selected node, when the opticalsignals to be transmitted do not have the selected powercharacteristics.
 17. The method of claim 16, further comprising a stepof repeating the steps of transmitting, determining, and re-configuringuntil the optical signals to be transmitted from the selected node haveselected signal-to-noise ratios.
 18. The method of claim 16, furthercomprising a step of repeating the steps of transmitting, determining,and re-configuring until selected signal channels of the optical signalsare balanced to have selected power ratios.
 19. The method of claim 16,further comprising a step of repeating the steps of transmitting,determining, and re-configuring until the optical signals transmit fromthe selected node have a consistent output power per wavelength.
 20. Themethod of claim 16, wherein the step of re-configuring comprises stepsof: re-configuring the selected node, when the optical signals do nothave the selected power characteristics; storing re-configurationinformation generated when the node is re-configured; and using thestored re-configuration information to adjust the selected node tocompensate for power level changes that occur in the network due achange in network conditions.
 21. An optical network operable to managesignal power levels of optical signals in an optical network so that theoptical signals have selected power characteristics, wherein the opticalnetwork includes a plurality of nodes that receive and transmit theoptical signals over optical fibers, the optical network comprising:means for configuring one or more nodes based on configurationparameters; and means for performing steps of: accessing powerparameters relative to one or more nodes; determining from the accessedpower parameters if the optical network is fully configured so that theoptical signals have the selected power characteristics; andre-configuring one or more nodes, when the optical signals do not havethe selected power characteristics.
 22. The optical network of claim 21,further comprising means for repeating the steps of accessing,determining and re-configuring until the optical network is fullyconfigured so that the optical signals have the selected powercharacteristics.
 23. The optical network of claim 21, further comprisingmeans for repeating the steps of accessing, determining andre-configuring until the optical network is fully configured so that theoptical signals have the selected power characteristics, wherein theselected power characteristics occur when the optical signals have aconsistent output power per wavelength between neighboring nodes. 24.The optical network of claim 21, further comprising means for repeatingthe steps of accessing, determining and re-configuring until the opticalnetwork is fully configured so that the optical signals have theselected power characteristics, wherein the selected powercharacteristics occur when the optical signals have a selectedsignal-to-noise ratio.
 25. The optical network of claim 21, furthercomprising means for repeating the steps of accessing, determining andre-configuring until the optical network is fully configured so that theoptical signals have the selected power characteristics, wherein theselected power characteristics occur when selected signal channels ofthe optical signals are balanced to have selected power ratios.
 26. Theoptical network of claim 21, further comprising means for using thepower parameters to adjust a selected node to compensate for power levelchanges that occur in the network due a change in network conditions.27. The optical network of claim 21, further comprising means forreceiving the power parameters at a selected node from a selectedneighbor node.
 28. The optical network of claim 27, wherein the meansfor receiving comprises a step of receiving the power parameters at theselected node from at least one neighbor node, wherein the powerparameters includes a transmit power level parameter.
 29. A nodeoperable to manage signal power levels of optical signals in an opticalnetwork so that the optical signals have selected power characteristics,wherein the optical network includes a plurality of nodes that receiveand transmit the optical signals over optical fibers, the nodecomprising: means for configuring the node based on configurationparameters; and means for performing steps of: receiving power parameterinformation describing power levels of the optical signals to bereceived at the node; determining from the power parameter informationif the optical signals to be received at the node have selected powercharacteristics; and re-configuring the node, when the optical signalsdo not have the selected power characteristics.
 30. The node of claim29, further comprising means for repeating the steps of receiving,determining, and re-configuring until the optical signals to be receivedat the node have the selected power characteristics.
 31. The node ofclaim 29, further comprising means for repeating the steps of receiving,determining, and re-configuring until the optical signals to be receivedat the node have a selected signal-to-noise ratio.
 32. The node of claim29, further comprising means for repeating the steps of receiving,determining, and reconfiguring until selected signal channels of theoptical signals are balanced to have selected power ratios.
 33. The nodeof claim 29, further comprising means for repeating the steps ofreceiving, determining, and re-configuring until the optical signalsreceived at the node have a consistent output power per wavelength. 34.The node of claim 29, wherein the means for performing the step ofre-configuring comprises means for performing steps of: re-configuringthe selected node, when the optical signals do not have the selectedpower characteristics; storing re-configuration information generatedwhen the node is re-configured; and using the stored re-configurationinformation to adjust the selected node to compensate for power levelchanges that occur in the network due a change in network conditions.35. The node of claim 29, further comprising means for performing stepsof: transmitting power parameter information describing power levels ofthe optical signals to be transmitted from the selected node;determining if the optical signals to be transmitted from the selectednode have selected power characteristics; and re-configuring theselected node, when the optical signals to be transmitted do not havethe selected power characteristics.
 36. The node of claim 35, furthercomprising means for repeating the steps of transmitting, determining,and re-configuring until the optical signals to be transmitted from thenode have a selected signal-to-noise ratio.
 37. The node of claim 35,further comprising means for repeating the steps of transmitting,determining, and re-configuring until selected signal channels of theoptical signals are balanced to have selected power ratios.
 38. The nodeof claim 35, further comprising means for repeating the steps oftransmitting, determining, and re-configuring until the optical signalstransmit from the node have a consistent output power per wavelength.39. The node of claim 35, wherein the means for performing the step ofre-configuring comprises means for performing steps of: re-configuringthe node, when the optical signals do not have the selected powercharacteristics; storing re-configuration information generated when thenode is re-configured; and using the stored re-configuration informationto adjust the node to compensate for power level changes that occur inthe network due a change in network conditions.
 40. A network elementoperable to manage signal power levels of optical signals in an opticalnetwork so that the optical signals have selected power characteristics,wherein the optical network includes a plurality of nodes that receiveand transmit the optical signals over optical fibers, the networkelement comprising: node logic that includes an optical receiver toreceive at least a first portion of the optical signals and an opticaltransmitter to transmit at least a second portion of the opticalsignals; and power management logic coupled to the node logic andcomprising: an input to receive configuration parameters to configurethe network element; a processor operable to perform steps of: receivingpower parameter information describing power levels of the first portionof the optical signals to be received at the optical receiver;determining from the power parameter information if the first portion ofthe optical signals to be received at the optical receiver have selectedpower characteristics; and re-configuring the node logic, when theoptical signals do not have the selected power characteristics.
 41. Thenetwork element of claim 40, wherein the selected power characteristicsoccur when the optical signals have a consistent output power perwavelength.
 42. The network element of claim 40, wherein the selectedpower characteristics occur when the optical signals have selectedsignal-to-noise ratios.
 43. The network element of claim 40, wherein theselected power characteristics occur when selected signal channels ofthe optical signals are balanced to have selected power ratios.
 44. Thenetwork element of claim 40, wherein the processor is further operableto transmit a request to a second network element to adjust power levelsof the optical signals transmitted from the second network element. 45.The network element of claim 40, wherein the processor is furtheroperable to perform steps of: receiving a request to adjust power levelsof the optical signals transmitted from the network element; andadjusting the power levels of the optical signals transmitted from thenetwork element in response to the request.